• The DERMIS and its DERIVATIVES
• The dermis is generally much thicker than the epidermis and lies more deeply. It is
made of a fibrous mass of connective tissue (collagen) and is of mesodermal
origin. It may directly produce dermal bone. The dermis is important in defense
against injury and in the maintenance of body heat. Deeper regions of the dermis
often contain fatty deposits, smooth muscle, blood vessels and nerves.
Chromatophore cells are sometimes epidermal, but usually dermal in origin. They
secrete melanin, which can be passed to the stratum corneum of skin and to hair
shafts to produce colour and block harmful sunlight.
• Dermal Bone
• Once present in some extinct fish - Ostracoderms with a complete head shield,
Placoderms with a broken head shield and body armor. Now demonstrated in
Turtle dermal bone, antlers, and in the dermal armor of Armadillo. In antlers the
velvet is epidermal in origin and shapes and provides blood to the dermal bone.
Once grown, the velvet is shed and only the bone remains. Antlers are found in
deer, elk, moose and their relatives, often only in males. They are shed annually.
• In most modern vertebrates, dermal bone is formed from embryonic mesenchyme
by extra membranous ossification, and contributes to the skull and skeleton, rather
than being manifested externally. An exception is teeth, which are partly derived
from dermal bone.
Hair & Fur
• Fish Scales
• Fish scales are also called dermal scales since they are derived mainly from the
• 1) Cosmoid Scales: Found in Placoderms (extinct) as plates, and also typical of the
Lobe Finned Fishes or Sarcopterygii, (Choanichthyes). Extinct fish had scales of
enamel, cosmine and bone with pulp cavities. Modern ones, like Coelocanth and
the lung fish have calcified fibers so this type of scale is almost extinct. Placoid
Scales: Made of enamel (epidermal) and the dermal derivatives, dentine and bone
with a pulp core. Typical of cartilaginous fishes. Placoid scales are responsible for
the rough feeling of dogfish skin.
• Ganoid Scales: Sturgeon, called scutes, and the scales of the Gar Pike Made of
multi-layered enamel called ganoin over lamellar bone. Primitive (now extinct)
species also had a cosmine layer and vascular bone with pulp, but these were lost
in modern day examples.
• Teleost (bony fish) scales
• These are thin scales of dermal bone. They have a thin covering of epidermal tissue
over them. It is derived by reduction (loss) of parts of a ganoid scale. There are two
types depending on their shape.
• Cycloid Scales: A round ended scale.
• Ctenoid Scales: A comb shaped end is characteristic of this scale type.
Fish scales (gar)
Ctenoid fish scale
Cycloid fish scale
More snake scales
• Teeth are composed of three main parts. Enamel, the hardest substance in
the body, covers the tooth surface. It is epidermal in origin. Dentin is
similar to bone in structure but is harder. It is located beneath the enamel
and forms the walls of the third component of teeth, the pulp cavity. These
are of dermal origin.
• Teeth are used to catch and hold prey, to crush hard shells and, in some
higher vertebrates, to carry out mechanical digestion of food in the mouth.
• Examine the teeth of Shark on demonstration. Note that mollusk-eating
sharks have blunt teeth, while others have a cutting edge. Despite such
variations, the scales formed on dogfish skin and the teeth found in its
mouth are both made of enamel, dentin and bone with a pulp core, i.e.
shark teeth are modified placoid scales. Teeth of higher vertebrates are
thought to have evolved from bony dermal scales similar to dogfish placoid
scales. They have a complex embryonic origin involving both the epidermis
and the dermis. Interestingly, their development bears some resemblance
to that of hair and feathers. Mesenchyme cells collect in the dermis to
form dermal papillae, which are instrumental in the production of dentin
and go on to form the pulp of the tooth. Enamel is produced by the
epidermis. The tooth in mammals is held in place by cement, which is a
non-vascular form of bone.
Wear Patterns of Teeth are Functionally Important
Enamel is > 95% inorganic matter; it is the hardest substance in vertebrate bodies
Enamel is harder than dentine
Dentine is harder than cement
These properties mean that teeth can be “self-sharpening”
A) Tooth Disposition (Where are they found?)
Teeth or dermal structures, which are tooth-like, may be found
wherever ectoderm occurs in the mouth area. For this reason teeth can
occur outside the jaws as in the pharyngeal teeth on the bony
elements of the branchial bars, or outside the buccal cavity as teeth in
the sawfish. See Amia, Pike and Sawfish.
Teeth occur mainly on the jaw bones, with some occurrence on the
palate. Examine the skulls of Frog (Anurans) and the Salamander
Necturus (Urodeles) on demonstration.
A few birds have teeth on their beaks.
Teeth occur only on the jaw bones, i.e. on the dentary, premaxilla and
maxilla. This is the case in reptiles also.
Some Important Terms for Teeth
Polyphyodont - multiple generations of tooth replacement (most vertebrates)
Diphyodont - two sets of teeth: milk and permanent (most mammals; incisor, canine
and premolar teeth are replaced)
Monophyodont - a single set of teeth (e.g., cetaceans)
Homodont - teeth of similar shape along jaw
Heterodont - teeth of different shape along the jaw
Tooth plate or Toothplate - at least two uses are common:
1. Many individual teeth fused together at their bases; separate cusps are still
visible (e.g., in pharynx of fishes)
2. Fusion of individual teeth during ontogeny: separate cusps may not still be
visible (e.g., lungfishes, chimaeras)
•B) Tooth Insertion (How they are attached).
•There are three methods of tooth insertion. Examine the
demonstration material and identify the following methods of
•1) Acrodont (acro=end)
•The teeth are fused by their bases to the outer surface of the
jaw. This condition occurs in most Teleosts (bony fish) and can
be also seen in the sharks. The teeth are not firmly rooted and
are easily lost and replaced. Teeth that are continually replaced
are called polyphylodont (poly=many).
•2) Pleurodont (pleur=side)
•The teeth are fused by one side to the inner surface of the jaw.
This occurs in the Salamander Necturus, frogs, and in the
Lizards. Most birds have no teeth but mergansers, Peking duck
and a few others have pleurodont teeth. Pleurodont teeth are
•3) Thecodont (theca=cup)
•The teeth are placed on the crown of the jaw in a socket. A
tooth may have a single root, as in the alligators, or several
roots as in the molars of Mammals.
Frog – vomerine teeth
• C) Tooth Differentiation (How they differ).
• The shape of the teeth in the Fishes, Amphibia and Reptiles is relatively
constant in any one group. Functional adaptations occur in the size, and in
specialization such as poison ducts in the fangs of snakes. Study the
demonstration material in the above groups and notice the similarity in
shape - called the Isodont or Homodont (iso/homo = equal) condition.
• Dentition in Mammals is generally Heterodont (hetero=different). The
teeth are modified in shape and size to serve specialized functions. Study
this modification in the Wolf skull. Notice incisors (cutting), canines
(piercing), premolars (grinding) and carnassials (shearing), and molars
(crushing). Examine the general demonstration of mammalian teeth. Notice
the adaptations are correlated with food habits. Compare the Carnivores,
Herbivores, Omnivores (human and pig) and Insectivores (mole and
Types of Mammalian Teeth and Dental Formulae
Incisor teeth (I), typically these are replaced
Canine teeth (C), typically these are replaced
Premolar teeth (P), typically these are replaced
Molar teeth (M), typically these are not replaced
Formulae are expressed as type # in upper jaw/# in lower jaw
I 5/4, C 1/1, P 2/2, M 4/4 = opossum
I 2/2, C 1/1, P 2/2, M 3/3 = humans
Carnassial Pair: P4-M1
• In the Carnivores note the specialized long and sharp canine teeth, and
the last premolar of upper jaw and first molar of lower jaw, which have
been modified as carnassials used for cutting. Within the group notice
variations of teeth used for cutting, piercing, incising and gripping.
• Examine upper and lower jaws of the Herbivores, and note the
differences, a large gap, the diastema (=internal) and often a horny upper
pad - check the horse, deer, rabbit, ox, and beaver. Examine the
Omnivore dentition and compare with Carnivores, Herbivores and
• Bears are Omnivores. Note, however, that their overall tooth
differentiation resembles that of carnivores.
Turtle scutes and dermal bone
Armadillo dermal epidermis