Comparative Anatomy Early Embryo

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					Comparative Anatomy
    Early Embryology

      Chapter 5

        Part 7
                   Vertebrate Egg

              Figure 7.1. Cledoic egg.

   Amniotic egg- amnion present
   Reptilian egg- possesses shell(cleidoic)
                        Egg Type

   Microlecithal egg- small amount of yolk
       Mammals
   Mesolecithal egg- moderate amount of yolk
       Amphibians
   Macrolecithal egg- large amounts of yolk
       Reptiles, birds, sharks
                  Types of Cleavage
   Holoblastic- division
    into two equal sized
    cells (e.g., in mammals)
   Meroblastic- restricted
    to periphery, usually in
    embryos with large
    amounts of yolk.
    Meroblastic discoidal -
        Blastodiscs occur in
    some fishes, reptiles, birds,   Figure 7.2. Blastodisc.
    and monotremes
    Amphibian Embryogenesis

Figure 7.3. Frog development; stages of embryogenesis (book fig. 5-12)
Figure 7.4.
                              Cleavage Stages

         Initial: fertilized egg      2 cell stage;   4 cell stage;
           with fertilization         1st cleavage    4 blastomeres
         membrane (arrows)

        8 cell stage;               32 cell stage;    64 cell stage;
        micromeres and              morula            blastula with
        macromeres                                    blastocoel cavity
        16 cell stage (not shown)
              Cleavage Stages (cont’d.)

Figure 7.5.

   Cells push inward to form gastrula
   Eventually eliminates blastocoel

Figure 7.6. Gastrulation.
      Archenteron- primitive gut
      Blastopore
           Gives rise to anus in
           Gives rise to mouth in
      3 primary germ layers         Figure 7.7. Cross section of frog gastrula.
Figure 7.8. Early frog gastrula.

   Dorsal lip - invagination of cells
      Move around yolk cells

      Yolk plug

   Notochord forms from mesodermal cells
   Neural plate thickens and
    pushed inward
   Neurectoderm- gives rise to
    nerve tube
   Neural crest cells- between
    nerve tube and ectoderm
       Dorsal root ganglion, branchial
        cartilages cells, and pigment cells
       Anterior cells- dermis of face,
        cephalic armor, sensory capsules

                                              Figure 7.9. Embryonic neurulation.
Figure 7.10. Neural crest cell differentiation. (Table 5.2; page 189).
                         Dorsal Mesoderm

Figure 7.11.

          Dermatome- associated with ectoderm
                  Dermis in most of body
          Myotome
                  Skeletal muscle
          Sclerotone- associated with nerve tube
                  Skeletal and vertebral column
   Dorsal mesoderm (somite)
    splits to form coelom cavity
      Somatic mesoderm -
        bound to ectoderm
      Splanchnic mesoderm-
        bound to endoderm
   Somatopleure - somatic
    mesoderm meets ectoderm
   Splanchnopleure -
    splanchnic mesoderm
    meets ectoderm

                               Figure 7.12. Mesoderm specialization (book Fig. 5.6).
    Dorsal Mesoderm Differentiation

Figure 7.13.

   Dorsal mesoderm (somite)- Epimeric mesoderm
   Intermediate mesoderm- Mesomeric mesoderm
   Lateral plate mesoderm- Hypomeric mesoderm
   Primary Germ Layers

Figure 7.14. Formation of the three primary germ layers.
               Germ Layers (cont’d.)

Figure 7.15. Organs derived from the germ layers.
Structures formed from
the three germ layers.

            Figure 7.16.
Ectodermal placodes
in a representative

        Figure 7.17.
    Extraembryonic Membranes

Figure 7.18. Extraembryonic membranes of cledoic egg.
Extraembryonic Membrane Formation in a Bird

   Figure 7.19. Extraembryonic membranes.
             Principles of Embryology

Figure 7.20. Embryological development.

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