LAB Mink Dissection Manual

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LAB Mink Dissection Manual Powered By Docstoc
               TABLE OF CONTENTS

Introduction                                  i
Anatomical Terms and Dissection Instruments   ii
The Integumentary System                      1-
The Muscular System
The Circulatory System
The Respiratory System
The Digestive System
The Excretory System
The Reproductive System
The Neuroendocrine System
The Skeletal System
Special Sense Organs

      Native mink are common throughout most of the United States, Canada,
and Alaska, except in the Southwest and very far north. Domesticated mink are
raised on ranches, found mostly in the Great Lakes regions, for their fur pelts.
Furriers fashion these pelts into coats, shawls, and other clothing goods in what
comprises a multi-million dollar industry. Since the pelt is what holds the most
value, the carcass of mink are sold at small cost to rendering plants, which
harvest mink oil, or to biological supply companies, which sell as dissection

        The Genus Mustela includes weasels, ferrets, and mink. Mustela means
“little mouser” and, at one time, mink, and more commonly ferrets, were used to
hunt rats and mice. The mink is a member of the Family Mustelidae. Other
members of this family are the martens and fishers, wolverines, badgers,
skunks, and otters. This family is commonly referred to as musk carriers. The
skunk has developed this adaptation most effectively, but the mink also has a
very powerful, penetrating, and lasting effluvium (scent). The ranch mink
represents a domesticated version of the North American mink, Mustela vison.
Domesticated meaning not so much being “tamed”, because they are far from
that, but rather that the mink is under man’s control as far as its breeding, care,
and profit is concerned.

      The mustelids belong to the Order Carnivora, the flesh eaters, and in the
suborder Fissipedia indicating a separation between toes as contrasted to
Pinnipedia, where the toes are webbed, forming flippers. Common carnivores
include bears, raccoons, wolves, cats, seals, and walruses. All of these are
grouped with other hairy animals in the Class Mammalia. They are vertebrates
in the Phylum Chordata.

      As humans are also Mammalian vertebrates, we can learn much
information about the structures and functions of our own bodies by dissecting
mink. Aesthetically, the mink is most impressive as an anatomical specimen.
Its powerful musculature makes for interesting dissection, particularly for those
interested in human anatomy. The dissection of the mink will be worthwhile for
students studying in many areas of biology from high school biology to zoology
to comparative anatomy.

   Use this dissection manual to help you make the most of your dissection,
  including for identification purposes and to help you learn the structure and
        function of each system. And, remember to have fun and learn!

                              ANATOMICAL TERMS
           Cranial: Toward the head                              Caudal: Toward the tail
            Dorsal: Toward the back                             Ventral: Toward the belly
   Proximal: Toward the point of attachment               Distal: Away from point of attachment
          Medial: Toward the midline                           Lateral: Away from midline
       Anterior: Toward the front (head)                    Posterior: Toward the back (tail)
  Superficial: The surface or near the surface                  Deep: Below the surface
  Transverse: Across the animal; Plane that            Peripheral: Away from the center or surface
      divides cranial and caudal portions
 Sagittal: Plane that divides right and left sides     Frontal: Plane that divides into ventral and
                                                                    dorsal portions
                      Right and Left: Always refer to the animal’s right and left

                        DISSECTION INSTRUMENTS
Scalpel: A blade; used for cutting through  Tweezers: Used to hold tissue away from
muscle and thick tissue (do not use on bone the incision (do not use on delicate tissue!)
or delicate tissue!)
Scissors: Used for cutting through thin         Probe: A blunt metal tool; used for
organs and tissue (do not use on muscle or      sweeping away connective tissue and lifting
bone!)                                          up organs
Dissecting Needle: A sharp metal tool;          Ruler: Used for measuring organs, bones,
used for pinning back tissue.                   blood vessels, etc.
Bone Shears: Heavy duty “scissors”; used to cut through bones.
                          The Integumentary System
        The integument, or skin, provides the outer covering of the body. The integumentary
system includes the skin and its various derivatives such as glands, hair, scales, and
claws. This is the part of the animal that meets the world and must protect the body from
heat, cold, abrasion, ultraviolet radiation, desiccation (drying out), and a host of bacterial and
other lively invaders. It also must be sensitive to environmental stimuli such as pressure,
pain, heat, cold, and touch so that the whole body may respond to these physical factors.
The skin can also function in excretion of certain waste or absorption of certain chemicals,
and has other specific functions for some animals. In every animal, the integument is an
important system to the total economy of the organism.

The Epidermis
       The outer layer, or epidermis, consists of stratified epithelium cells divided into 5
layers. The stratum basale is the innermost layer of the epidermis. This is where new cells
are continually and are pushed toward the surface. This layer also gives rise to the skin
glands and hair, as well as to the epidermal components of nails and claws. The stratum
spinosum is directly above the stratum basale. The stratum granulosum follows the
stratum spinosum and is named as such because these cells have granular cytoplasm. The
stratum lucidium is immediately deep (beneath) the stratum corneum. It is named as such
since this layer’s cells have clear and enucleate cytoplasm. All cells are produced in the
stratum basale, forced toward the surface where they die, and become cornified by the
deposition of keratin (a type of protein). These cells form the stratum corneum (the
outermost layer of the skin). Cornified skin cells are constantly sloughing its outer, dead
layers and being replaced by cellular proliferation in the stratum basale (the inner most layer).

         Hair is a unique epidermal derivative found only in mammals. Hair grows from a pit-
like hair follicle which extends into the subcutaneous tissue of the dermis. The hair in the
follicle is called the root and the exposed hair is called the shaft. The root is enlarged into a
bulb at the bottom of the follicle and fits into a dermal papilla that nourishes the rapidly
dividing cells in the bulb. Attached to the follicle are arrector pili muscles. When these
muscles contract, the hair stands on end and causes “gooseflesh”.

       In mink, the quality of the fur depends on the degree of development of the underfur,
as well as color. As winter approaches, the underfur begins to grow from shallower follicles.
When it is fully developed, it is prime and it is the best time to harvest the pelt. Interspersed
among the hair of the underfur are long, coarse guard hairs which grow from deep follicles.
These are removed from seal and mink pelts, for example, but are kept in fox pelts.
Pigmentation of the skin and hair depends on the deposition of melanin in the basal cells of
the stratum germinativum. In mink, color is of great economic importance and, therefore,
mink breeders generally select for fashionable colors.

         Sebaceous glands are associated with hair and secrete oil, or sebum, into the
follicle, helping keep the hair supple. Oily guard hairs of the mink are effective water
repellents. Some sebaceous glands open directly to the skin surface.

       Sudoriferous or sweat glands open directly to the skin. In mammals, their primary
function is in temperature regulation (through water’s high heat of vaporization) and in
excretion. Ceruminous glands are modified sweat glands that produce ear wax. In many
mammals, sudoriferous glands produce pheromones, which may attract mates.

        The anal scent glands of the mink are either modified sweat or sebaceous glands
associated with the rectum that produce a foul-smelling musk. Be extraordinarily careful that
you do not cut through these glands in your dissection. If you do, you will notice a profoundly
horrific odor. Take the specimen outdoors immediately.

       Mammary glands are modified sweat glands that produce milk after the young are
born. Their development and secretory activity is dependent on hormones. The mink has six
mammae, or breasts. These mammae are actually accumulations of small ducted glands
called alreolar glands, each with a duct leading to the surface and forming an elevated
region called the nipple.

       Claws, like nails and hooves, are epidermal derivatives at the distal ends of the digits.
The claws of the mink are partially retractable. The structure of the claw consists of a dorsal
plate, called the unguis, and a ventral plate, or subunguis. The unguis is the better
developed. In the nail, the subunguis is very reduced and the unguis is broad and flat. In the
hoof, the unguis surrounds the subunguis.

The Dermis
        The dermis is the inner layer of the skin. It is much thicker than the epidermis,
consists largely of fibrous connective tissue, and is the raw material of leather. The dermis
provides the support for the epidermis and the structural framework for the blood and
lymphatic vessels, nerves, and muscle fibers. The dermis immediately below the epidermis
has small elevations, or papillae, that contain capillaries and sometimes receptors. These
papillae on the palms of the hands and soles of the feet are in rows and improve the grip on
hairless areas. They are called friction ridges, which are useful in man as a means of
identification. In mink, the foot pad is a comparative derivative.

The Hypodermis
       There is a variable layer of fat in the subcutaneous (hypodermis) layer fat beneath
the dermis. This layer contains loose connective tissue (to the skeletal muscles) and
adipose tissue for lipid storage. In the mink, this fatty layer, the panniculus adiposus, is
extensively developed at the time of pelting. This is a useful bi-product for making an oil
used in fine cosmetics and for conditioning leathers.

                              The Muscular System
        Mammals perform a variety of actions such as running, flying, jumping, and digging.
These activities are the result of the contraction of skeletal muscles, which move segments
of the limbs and body. There are more than 450 skeletal muscles in the mink. Other types of
muscle found in mammals are visceral (smooth) muscles, which act on parts of the
digestive tract and blood vessels, and cardiac muscle, which is restricted to the heart.
        As a muscle contracts, it shortens and performs work. The work or movement that
occurs is called the action of the muscle. In order to accomplish an action, a muscle pulls
one attachment of the muscle toward the other. One of the muscle’s attachments is called
the origin and the other is called the insertion. The origin is usually on a fixed or immovable
bone and the insertion is on a moveable bone. Often, however, both of the attachments are
on movable structures. When this is the case, the actual movement depends on “fixing” on
attachment so that the other is moved. Midway between the origin and insertion of most
muscles is a thickened area called the belly or venter. Most muscles are attached by thick
connective tissue tendons at their origin and insertion, but others may have a fleshy
attachment. A few muscles attach by a broad sheet of connective tissue called an
aponeurosis. Unless they lie in the midline of the body, all muscles are paired.

Types of Muscles and their Actions
       Muscles are categorized by their action (function) and are arranged in antagonistic
pairs or sets. An antagonistic muscle performs the opposite function of its pair.
                                      Action                              Example of Action
              Flexion is the reduction of the angle between two
  Flexors     bony elements in a joint. This takes place in the            Bending the knee
              sagittal plane
              Extension is the increase of the angle between two
Extensors     bony elements in a joint. This takes place in the          Straightening the knee
              sagittal plane
              Adduction is the movement of a structure toward           Moving arms toward the
              the midline in the frontal plane                             front of your body
              Abduction is the movement of a structure away                Spreading out the
              from the midline in the frontal plane                              fingers
              Rotation is the movement of a body part around the         The hand and forearm
 Rotators     long axis. Pronation is the term for medial rotation            when using a
              and supination is the term for lateral rotation.                 screwdriver
                                                                             Shrugging the
 Elevators    Elevation is lifting or raising a part of the skeleton
                                                                          Opening the mouth
Depressors Depression is lowering a part of the skeleton
                                                                        (mandible moves down)
              Constriction/dilation is the closing or opening,            Opening/closing the
              respectively, of a ring of muscle around an opening                  anus

Naming Muscles
        Muscles are named for their (1) location in the body, (2) shape, (3) origin and insertion,
(4) size, (5) action/function, (6) position, or a combination of these characteristics.
                             The Circulatory System
        The circulatory system consists of a closed system of vessels that transport nutrients,
wastes, hormones, gases, and cells within the body. The cells transport gases, repair
wounds, and fight infection. The heart pumps the fluid blood, moving it in a circular manner
carrying nutrients and oxygen to the tissues and carrying away carbon dioxide and waste
products. In addition to transporting nutrients, gases, and wastes, the blood also transports
heat. Blood is warmed by the heat generated during muscle contraction and cooled in the
skin that is in contact with the air. These blood vessels are more easily seen if injected with
colored latex; red latex is used to inject the arteries, blue latex for the veins, and yellow latex
for the hepatic portal system.

The Heart – External
        The heart lies in the pericardial sac. It feels firm to the touch. The anterior end is the
base and the posterior end is the apex. The heart is divided into four chambers: two atria
(right and left) and two ventricles (right and left).

       The atria of the heart receive blood from the lungs or body. Each atrium has an
auricular (“little ear”) pouch, which are small muscular flaps. The right atrium receives
deoxygenated (oxygen-poor) blood from the anterior (cranial) vena cava and posterior
(caudal) vena cava and from the coronary sinus after the oxygen in the blood has been
used by the body tissues. The left atrium drains oxygenated (oxygen-rich) blood from the
lungs via the pulmonary veins. The pressure of the blood in these chambers eventually
forces the blood into the ventricles.

       The muscular caudal portion of the heart consists of two ventricles separated
internally by an interventricular septum and externally by a shallow interventricular
sulcus. Note that the left ventricle is larger and more muscular than the right ventricle.
This is because the left ventricle must pump with enough force for the blood to reach the rest
of the body whereas the right ventricle only pumps blood back to the lungs to be re-
oxygenated. The right ventricle does not reach the apex of the heart. A deep coronary
sulcus marks the external separation of the atria and ventricles. Blood passes to the
pulmonary artery from the right ventricle and to the aorta from the left ventricle.

The Heart – Internal
       Note that the walls of the ventricles are much thicker than those of the atria and that
the right ventricular wall is thinner than the left. The trabeculae carneae are the muscular
bands on the inner wall of the ventricles. The papillary muscles are similar to the
trabeculae carneae, but with tendons (chordae tendineae) attached to them and to the cusps
of the atrioventricular valves.

       The ventricular chambers are separated from the atria and from the pulmonary artery
and aorta by valves. These valves prevent backflow of blood into the atria and will only open
when the pressure inside the atria reaches a particular level. The tricuspid valve separates
the right atrium from the right ventricle. The bicuspid (or mitral) valve separates the left
atrium from the left ventricle.        The tricuspid and bicuspid valves are termed the
atrioventricular valves. The semilunar valves, named for their crescent moon shape,
separate the aortic arch from the left ventricle and the pulmonary arch from the right ventricle.
Blood Vessels
       The blood vessels that carry blood away from the heart are called arteries. Blood
vessels that return blood to the heart are called veins. The walls of the arteries are more
muscular and thicker than veins. Many veins have one-way valves that prevent backflow of
blood (since the blood mostly travels against the force of gravity to return to the heart). The
compression of skeletal muscle on veins helps move the blood in these vessels. Some blood
spaces lined with endothelium are called sinuses. So that the blood may be circulated, the
arteries branch into smaller arteries, then arterioles, then into microscopic capillaries.
Exchange of materials between the blood and tissue fluid occurs through the capillary wall.
Capillaries complete the circulatory pathway by then connecting to veins. It is easiest to
examine the venous system first because much of it lies ventral to the arterial system.

The Venous System
       The cranial vena cava, or precava, is a single, large vessel formed by the union of
the right and left

The Arterial System
        The systemic aorta curves left dorsally from the cranial end of the heart as the aortic
arch. It then runs caudal as the thoracic aorta. Arteries will be injected red in your
specimen. The coronary arteries (right and left) branch from the aorta just cranial to the two
ventral cusps of the left semilunar valve and serve the heart muscle. The right coronary
artery turns toward the apex of the dorsal surface, and the left coronary artery branches to
the ventricular apex on the ventral surface of the ventricles. Both vessels lie in the
interventricular sulcus.

         The brachiocephalic artery is a single, unpaired vessel arising from the base of the
aortic arch. The brachiocephalic artery gives rise to the right and left common carotid
arteries and the right subclavian artery. The common carotid arteries extend cranial on
each side of the trachea to their division at the level of the mastoid process into internal and
external carotids. Each common carotid artery also branches to small vessels of the
esophagus and trachea. The right subclavian artery branches from the brachiocephalic
artery together with the common carotid arteries and passes out of the thoracic cavity at the
first rib.

       The left subclavian artery is a direct branch of the aortic arch just distal to the
brachiocephalic artery. Otherwise, the two subclavian arteries (right and left) are similar.
Each traverses the axilla as the axillary artery and continues into the forelimb as the brachial
artery. The subclavians have three major branches: the vertebral arteries (which branch
from the subclavian at the base of the neck and pass directly through the vertebrae and serve
the brain), the internal thoracic arteries (which branch from the subclavian at the first rib
and send branches to the musculature of the ventral chest region), and the costocervical
trunks (which branch from the subclavian and serve the neck and shoulder muscles, lymph
nodes, salivary glands, skin, and skin muscles of the neck).

       The axillary arteries are a continuation of the subclavian arteries through the axilla.
They give off a major branch, the subscapular artery, and then proceeds into the arms as
the brachial artery. This passes through the pectoralis profundus between the biceps and
triceps muscles, finally branching in the forearm into the radial and ulnar arteries.
        The dorsal aorta caudal to the aortic arch and continuing through the thoracic cavity is
the thoracic aorta. In the abdominal cavity, the thoracic aorta continues as the abdominal
aorta. Follow this vessel through the diaphragm and carefully clean away the connective
tissue surrounding the artery. The intercostal arteries branch from the thoracic aorta and
serve the intercostal musculature (muscle between the ribs). The esophageal arteries
branch from the thoracic aorta to the esophagus. The phrenic arteries branch from the
aorta and serve the diaphragm. The celiac artery is a large, unpaired branch of the
abdominal aorta serving the viscera at the cranial end of the abdominal cavity. The branches
of the celiac artery are named according to the visceral organ they serve, but they are all
interconnected. These branches include: the left gastric artery (to lesser curvature of the
stomach), the left lienal artery (to the pancreas), the right lienal artery (to the spleen), the
hepatic artery (to the liver, hepatic portal vein, and duodenum), and gastroduodenal artery
(to the stomach).

The Hepatic Portal System
       All of the veins previously described carried blood from a capillary bed to the heart. In
the case of a portal system of veins, blood is collected from the capillaries or sinusoids and is
delivered to another set of small vessels. The hepatic portal system takes blood from the
digestive tract, pancreas, and spleen to the liver. Lower vertebrates have a renal portal
system too.

       The hepatic portal vessel receives blood from the various abdominal visceral organs
that are suspended by the mesentery and empties to the sinusoids in the liver. The sinusoids
then drain to the central veins, hepatic veins, and finally the inferior vena cava. The portal
vessel is formed by four major veins: the gastroduodenal, the lienal (gastrosplenic), and the
cranial and caudal mesenteric.

       The gastroduodenal vein is formed by the right gastric vein (which drains the lesser
curvature of the stomach), the cranial pancreaticoduodenal vein (which drains the
duodenum and right lobe of the pancreas), and the right gastroepiploic vein.

       The lienal (gastrosplenic) vein is a large vein that joins the superior mesenteric vein
to form the hepatic vein. The gastrosplenic receives blood from smaller veins, including
several gastroepiploic veins from the stomach and great omentum, splenic veins from the
spleen, and pancreatic veins from the left arm of the pancreas.

       The cranial (superior) mesenteric vein is formed by numerous tributaries from the
small intestine (ileum and jejunum). These vessels form connections near their origin to
make anastomosing loops. The caudal pancreaticoduodenal vein and the vein very near
each other at the caudal end of the ventral pancreas. The first jejunal and ileocolic veins
enter the cranial mesenteric vein near each other and close to the duodenal-jejunal junction.

       The caudal (inferior) mesenteric vein drains the colon and has a few branches to
the last part of the large intestine. It is also a large vein and enters the cranial (superior)
mesenteric vein posterior to the gastrosplenic vein.

The Lymphatic System

        The lymphatic system is a part of the circulatory system that is difficult to observe in
most specimens. The system is well developed in mammals and functions as a path by
which liquids and leukocytes (white blood cells) from the tissues enter the general circulation.
Lymphatics consist of vessels paralleling the veins and are comparable to capillaries and
veins of the blood vessels. They differ from those of a true circulatory system in that the fluid
(lymph) is transported only toward the heart; that is, the lymphatic capillaries arise blindly in
the tissues. Also, lymphatic capillaries tend to be larger in diameter and more irregular than
blood capillaries, and the larger lymphatic vessels have thinner walls than veins do.

       Because the lymphatic vessels have thin walls, they were not injected in your
specimen. Other structures belonging to the lymphatic system include the thymus gland,
the spleen, the tonsils (located in the oral cavity and pharynx), and the lymph nodes.
Lymphatic organs are also important as hemopoietic (blood forming) tissues.

       The thymus gland is an irregular mass of tissue at the cranial end of the heart. In the
young, this structure may reach the larynx. Later it is a much smaller structure located at the
bifurcation (branching) of the bronchi.

         The spleen is a flat, elongate reddish organ suspended in the great omentum to the
left of the greater curvature of the stomach. The spleen consists of a tissue mass, the red
pulp, with nodules of white pulp scattered throughout that serve as germinal centers for the
production of lymph cells. Trabeculae of connective tissue containing blood vessels and
nerves extend into the red pulp from the outer capsule. These details may be seen more
easily by slicing a small section and observing under a dissecting microscope. The spleen is
a fetal blood-forming tissue but is not so in adults. Bone marrow forms most of the blood
solids (cells) in adults.

       The lymph nodes are numerous and are found in subcutaneous tissues and body
cavities. You may locate intestinal nodes easily by looking for pinkish swellings in the
mesentery. The lacteals are lymph capillaries of the intestine and drain to the intestinal
lymph nodes. They are responsible for collecting the products of fat digestion.

The Pulmonary Circulation
      The pulmonary aorta, after leaving the right ventricle, divides into left and right
pulmonary arteries. Blood is returned to the left atrium by groups of pulmonary veins.
The arrangement of these vessels is more easily seen once the heart is removed.

                            The Respiratory System
       The respiratory system functions as a gas exchange mechanism between the external
medium (air) and the blood. Oxygen diffuses across the lung membranes to the blood, which
carries it to the tissues. Carbon dioxide is acquired by the blood at the tissues and is
released to the medium by diffusion through the lung membranes. Oxygen is used by the
mitochondria of the cells during cellular respiration (metabolism of glucose). Carbon dioxide
is produced as a waste product of this same cellular metabolism. The respiratory system
comprises of the nose and nasal passages, pharynx, larynx, trachea, and lung and related

Upper Respiratory Tract
       The nose is the first part of the upper respiratory tract. The skin of the nose is hairless
and pigmented. A vertical groove divides the nose and extends ventral to form the philtrum,
or groove, of the upper lip. The nasal chamber is divided by a bone and cartilage (nasal
septum) into separate, parallel cavities. These cavities warm (or cool), filter, and humidify
the inhaled air. Air enters the nasal cavities through the external nares. Air then leaves the
nasal cavities through the internal nares at the posterior end of the nasal cavities and enters
the nasopharynx.
       Forming the roof of the nasal cavity is the ethmoid bone. This bone is perforated by
olfactory foramina forming a feature called the cribriform plate. Olfactory nerves pass from
the sensory epithelium of the nasal cavity to the olfactory bulbs of the brain through these
       The pharynx is the common chamber of the respiratory and digestive systems.
Embryonically, this area is highly vascularized and the epithelium gives rise to several
endocrine glands. The pharynx is broken into three major sections: the nasopharynx, the
oropharynx, and the laryngopharynx. The glottis is the opening to the larynx from the

Lower Respiratory Tract
        The larynx is the “voice box” that serves as a passageway for air, as a part of the
structures involved in vocalization, and as a valve. Its valvular function, using the glottis and
epiglottis, directs the passage of ingested materials and air into the esophagus and trachea,
respectively. The wall of the larynx is held rigid by five cartilages:
        The epiglottis cartilage projects into the pharynx above the glottis. The cartilage is
attached to the basihyoid and toward the head-end of the thyroid cartilage. It generally rests
above the soft palate to direct inhaled air to the trachea. During swallowing, it drops and
cups slightly to guard the glottis.
        The caudal border of the glottis is supported by small, paired arytenoid cartilages.
The vocal cords (folds) are attached to the arytenoid and epiglottal cartilages. There are
two pairs of vocal cords: the false, or cranial, pair and the true, or caudal, pair. Both are
folds of the mucous membranes lining the larynx.
        The center of the larynx is stiffened by a large, unpaired thyroid cartilage (shield-
shaped). It has paired articulations with the hyoid apparatus.
        Unlike the thyroid cartilage, the more caudal cricoid cartilage forms a complete ring
surrounding the larynx and is widest dorsally.
        The tracheal cartilages are U-shaped and holds open the trachea. The trachea is
also called the “windpipe”. It extends from the larynx to the primary bronchi and is held open
by about 60-70 U-shaped tracheal cartilages. The lining of the trachea is composed of
ciliated, mucous-secreting cells that keep the lining moist.
        The trachea bifurcates (branches) at the level of the heart, just after it enters the
thoracic cavity, to form the primary bronchi. One bronchus extends to each lobe of the
lungs. The bronchial tubes are supposed by U-shaped cartilages and lined by ciliated cells.
Within the lungs the primary bronchi form secondary and tertiary bronchi with cartilage
“rings”. The terminal bronchioles are the smallest division of the bronchi, they lack
cartilaginous support. Some of these have alveoli in their walls and are called respiratory
bronchioles. The respiratory or terminal bronchioles finally branch into alveolar ducts that
lead to alveoli or alveolar sacs. Gas exchange takes place through blood capillaries and

the alveolar walls. All alveolar ducts and bronchioles have visceral (smooth) muscle fibers
in their wall, but the alveoli and alveolar sacs do not.
        The lungs are found in the pleural cavity of the thoracic cavity. The serous membrane
covering the lung is the visceral pleura and that which lines the inside thoracic wall is called
the parietal pleura. The lobes of the lungs are named according to the division of the
bronchi rather than superficial fissures that appear to divide them. Thus, the right lung has
four lobes (cranial, middle, caudal, and accessory) and the left has only two lobes (cranial
and caudal), but the left cranial lobe is partially divided into cranial and caudal portions by an
incomplete fissure.
        Deoxygenated blood is carried from the right ventricle to the lungs via the pulmonary
trunk and arteries. The oxygenated blood is returned to the left atrium by the pulmonary
veins. There may be one or two veins for each lobe of the lung. An oxygenated supply of
blood is also required. This is supplied by the bronchial arteries that branch from the first
dorsal intercostal artery.
        Thoracic volume changes are used to move air into and out of the lung. This is
accomplished by a complex association of the diaphragm, intercostals, serratus dorsalis,
scalenus, transversus costarum, transverse thoracic, iliocostalis, and lateral abdominal
muscle sheets (obliques and transversus). When the diaphragm is contracted, the volume of
the lungs increases. This increase in volume decreases the air pressure inside the lungs,
making it lower than the pressure of the atmosphere. This causes air to be pushed into the
lungs (inhaling). When the diaphragm is relaxed, the volume of the lungs decreases, causing
an increase in air pressure in the lungs which results in air being pushed out of the lungs

                              The Digestive System
       The digestive system consists of many organs working together for the major purpose
of digesting food. Digestion is the process of breaking down large organic macromolecules
into their building blocks. The purpose for this is twofold. By breaking down the molecules,
they will be small enough to be absorbed into the bloodstream where their can use them.
Also, if one stops to consider an animal’s food was once another organism, the food
molecules are literally the macromolecules once used by the previous organism. By
digesting these molecules into their building blocks, the animal can use some of these
building blocks to construct its own macromolecules. An animal eats not only to get
molecules that can supply energy, but also to get molecules from which it can make its own
unique molecules.

Salivary Glands
        The parotid gland lies superficially beneath the skin and just ventral to the ear. The
parotid duct crosses the masseter muscle with branches of the facial nerve and a vein and
opens to the mouth opposite the last premolar tooth.
        The mandibular gland is ventral to the larger parotid at the angle of the jaw. The
mandibular duct opens through a small papillum on each side of the base of the frenulum
(a leaf-like flap of mucus membrane) of the tongue.
        The sublingual gland is a very small gland located between the digastricus and
mylohyoideus on one side and the styloglossus medially at the level of the angle of the
mandible. Its duct parallels that of the mandibular gland and opens next to it.

         The infraorbital (zygomatic) gland lies within the orbit, on the ventral part. This is a
fairly large gland, but it is difficult to expose. If the jaw muscles have been removed, the eye
can be pressed ventrally (down), forcing the gland from under the zygomatic arch. Its duct
enters behind the upper molar on each side of the head.
         The molar (buccal) gland is a very small gland located near the anterior corner of the
mouth in the angle formed by the anterior and posterior facial veins. Its duct parallels the
mandibular and opens at the same point.

Oral Cavity
       The vestibule is the area of the mouth between the lips, cheeks, and teeth. Teeth in
the upper jaw are called the palatal dentition and in the lower jaw are called the lingual
dentition. There are three incisors on each side of the upper and lower jaws. These are
followed immediately by one canine and then three premolars on each side on the top and
bottom. The last palatal premolar is a large tooth with a flat, cutting cusp. It meets with the
cusp of the large first lingual molar to form the carnassials, which are used to shear tough
tissues such as tendons, cartilage, and bone. Behind the last premolar of the upper jaw is a
single molar. In the lower jaw, the large first molar is followed by a very small second molar.
The dentition of the mink is specialized for feeding on flesh. Very little grinding is done as it is
in plan eaters, therefore the molar series is reduced by comparison. The dental formula of
mink is often written as:                    3 ● 1 ● 3 ● 1
                                             3 ● 1 ● 3 ● 2
       This formula indicates the number of incisor, canine, premolar, and molar teeth in each
jaw. It is interesting to compare this formula with human teeth and those of an herbivore.
       The tongue is very muscular, thick at its root, and thinner and narrower toward the
apex. Intrinsic tongue muscles(lingualis proprius) alter the shape of the body of the tongue.
The frenulum is the thin membrane on the midventral surface of the tongue holding the
tongue to the floor of the mouth. Cornified filiform papillae (spiny in shape) cover most of
the dorsal surface of the tongue. Toward the root of the tongue, there are also four to six
vallate papillae (columnar in shape) arranged in a “V”. A few fungiform papillae
(mushroom in shape) are also found, mostly posteriorly. The circumvallate and fungiform
papillae may have taste buds located in furrows or grooves of the papilla. Each taste bud
consists of elongate cells arranged around a central lumen (cavity) that opens to the papillary
furrow by a taste pore.
       The hard palate forms the anterior (front) roof of the mouth. It is marked by
transverse, corrugated ridges, or rugae. The posterior (back) continuation of the roof of the
mouth is the soft palate. The free border is overlapped by the epiglottis.

      The pharynx is the common chamber of the respiratory and digestive systems.
Embryonically, this area is highly vascularized and the epithelium gives rise to several
endocrine glands. The pharynx is broken into three major sections.
      The space above the soft palate is the nasopharynx. It opens anteriorly through the
choanae, or internal nares. This is the opening from the nasal chamber to the
nasopharynx. The Eustachian (auditory) tubes are found in the lateral walls of the
nasopharynx and they connect the cavities of the middle ear with the pharynx.
      The oropharynx is a passage for food entering from the oral cavity. The isthmus
faucium is the opening of the oral cavity to the pharynx. The palatine tonsils are very
prominent lymphatic tissue on the lateral border of the isthmus, on a flap immediately ahead
of the epiglottis.
       The laryngopharynx lies dorsal to the larynx (voice box) and esophagus and
originates at the base of the oropharynx. The opening from the laryngopharynx to the larynx
just ventral to the origin of the esophagus and held open by cartilaginous rings in its wall is
called the glottis. The epiglottis is one of the laryngeal cartilages. It acts as a valve to
direct swallowed materials away from the glottis and into the esophagus. The esophageal
opening lies dorsal to the glottis. It is the origin of the esophagus, which leads to the

Alimentary Tract
        The esophagus is a mucous-membrane lined tube that spans the 17-19cm from the
pharynx to the stomach. It is usually collapsed and lies dorsal to the trachea. Prior to
entering the cardiac portion of the stomach, it passes through the diaphragm.
        The esophagus leads directly to the stomach. This J-shaped organ, typical of a
carnivore, has three regions: the cardiac (the entrance of the esophagus), the fundic (the
large, middle, sac-like portion), and the pyloric (constricted caudal portion that opens to the
duodenum). The cardiac lining has mucous-secreting cells, but no enzymes are produced
here. The fundic portion secretes all the enzymes and hydrochloric acid (HCl) produced by
the stomach. The pyloric cells secrete mucous. The size of the stomach, as in other
carnivores, depends on how recently and how much the animal has eaten. If full, the
stomach may be very large. The anterior concave curve in the stomach is the lesser
curvature and the posterior, convex curve is the greater curvature. The longitudinal ridges
inside of the stomach’s lining are called rugae and increase surface area inside the stomach,
which help in digestion.
        The small intestine is about six times the body length of the mink (excluding the tail).
In humans, it is three to four times body length. The first part of the small intestine is called
the duodenum, about 10cm in length, receives the ducts of the digestive glands via a
duodenal papillum near the pylorus (the passageway between the stomach and the
duodenum). The muscularis mucosa is composed principally of circular visceral muscle
fibers in this region and is extremely thick. It forms the pyloric sphincter, which controls the
entrance to the small intestine. The epithelium of the duodenum (and all of the small
intestine) has numerous, tiny, finger-like projections called villi, which give the lining a soft,
velvety appearance. The right lobe of the pancreas is adjacent to the duodenum, which
helps distinguish this region from the next part of the intestine, called the jejunum.
        The jejunum is the second portion of the small intestine. The demarcation of the
duodenojejunal junction is a rather sharp flexure and usually the first part of the jejunum
appears thin walled and empty. The jejunum empties into the ileum, the third part of the
small intestine. There is no clearly recognizable junction between these two parts.
        The ileum is the remaining, terminal portion of the small intestine. It opens to the
large intestine by the ileocolic sphincter. The ileum is characterized by lymph nodules
(Peyer’s patches) in the submucosa. Enlargements on the surface of the ileum caused by
Peyer’s patches are usually grossly evident. The ileum ends at the colon. Both the jejunum
and ileum together have a total length of 140 cm.
        The large intestine, or colon, is so called because the lumen (opening) has a greater
diameter than the lumen of the small intestine. There is no cecum (pouch) at the beginning
of the mink colon, and its lining is not villiated. There are, however, longitudinal ridges that
function to increase the surface area. If the colon is empty, its diameter may be no larger
than the small intestine, but there may be feces present. The colon is not divisible into
ascending, transverse, and descending regions as it is in many other mammals. Instead, it is
a short, descending tube that ends in the rectum.
        The rectum is more muscular than the colon. In the female, the muscular vagina and
cervix are ventral to the rectum. In the male, the neck of the urinary bladder and prostate
gland are ventral to it. The epithelium of the rectum has a very dense population of goblet
cells that provide a mucinous lubrication for the feces.
        The anus is the very short termination of the alimentary tract. The mink has a pair of
anal glands that produce a bad-smelling musk and are usually removed during commercial
preparation of dissection specimens. If they have not been removed already, do not break
them open!

Digestive Glands
        The liver is the largest gland in the mink. The liver is divided into right and left halves
by the falciform ligament. This mesentery stretches from the liver to the diaphragm and is a
remnant of the ventral mesentery containing the obliterated umbilical vein of the fetus. The
left half of the liver consists of three lobes: left median lobe, left lateral lobe (which has a
notch on its dorsal surface for the esophagus and is the largest of all the lobes), and to the
right and left of the left median lobe, a quadrate lobe (which has a deep fossa for the gall
bladder). The right half also has three lobes, but the right median lobe is so large that it
obscures much of the other two. The right lateral lobe is dorsal to the right median lobe.
Together, the right median and right lateral lobes surround the small caudate (spigelian)
lobe (which extends posteriorly to form a pocket for the right kidney).
        The gall bladder lies in a cleft between the right median lobe and caudate. Bile
canaliculi run between individual liver cells and open to bile ductules that, in turn, drain into
hepatic ducts in the various lobes. The hepatic ducts form the left side of the liver; the right
and the caudate lobe join with the cystic duct to form the common bile duct that opens into
the duodenum. The common bile duct projects into the duodenum as the major duodenal
papillae, and its opening is controlled by a sphincter that surrounds the papillae.
        The pancreas is another large organ in the mink. It has a right lobe along the
duodenum and a left lobe next to the stomach and spleen. The cells of the pancreas are
arranged in groups similar to those of the salivary glands so their secretion flows into a
central cavity between the secreting cells (this arrangement is termed acinar). The acinar
cavity is drained by ducts that collectively drain (as pancreatic ducts from each lobe) into
either the common bile duct or an accessory duct, which drains directly into the duodenum
shortly after the first duodenal flexure. Some of the acinar groups have enlarged cells that
obliterate the central cavity and have no drainage duct. These bundles, known as
pancreatic islands (islets of Langerhans), secrete their products into adjacent blood vessels.
The pancreatic islands are endocrine glands, and their secretions are the hormones insulin
and glucagon.

                            The Excretory System
                          The Reproductive System
                         The Neuroendocrine System
                             The Skeletal System
Special Sense Organs


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