Comparative Anatomy Early Embryology

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Comparative AnatomyEarly Embryology

• Kardong
• Chapter 5
• Part 7

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Vertebrate Egg
Figure 7.1. Cledoic egg.

• Amniotic egg- amnion present
• Reptilian egg- possesses shell(cleidoic)

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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

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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, and monotremes

Figure 7.2. Blastodisc.
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Amphibian Embryogenesis
Figure 7.3. Frog development stages of
embryogenesis (book fig. 5-12)
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Cleavage Stages
Figure 7.4.
Initial fertilized egg with fertilization
membrane (arrows)
2 cell stage 1st cleavage
4 cell stage 4 blastomeres
8 cell stage micromeres and macromeres 16 cell
stage (not shown)
64 cell stage blastula with blastocoel cavity
32 cell stage morula
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Cleavage Stages (contd.)
Figure 7.5.

• Cells push inward to form gastrula
• Eventually eliminates blastocoel

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Gastrulation
Figure 7.6. Gastrulation.

• Archenteron- primitive gut
• Blastopore
• Gives rise to anus in deuterostomes
• Gives rise to mouth in protostomes
• 3 primary germ layers

Figure 7.7. Cross section of frog gastrula.
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Figure 7.8. Early frog gastrula.

• Dorsal lip - invagination of cells
• Move around yolk cells
• Yolk plug
• Notochord forms from mesodermal cells

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Neurulation

• 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.
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Figure 7.10. Neural crest cell differentiation.
(Table 5.2 page 189).
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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

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• 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).
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Dorsal Mesoderm Differentiation
Figure 7.13.

• Dorsal mesoderm (somite)- Epimeric mesoderm
• Intermediate mesoderm- Mesomeric mesoderm
• Lateral plate mesoderm- Hypomeric mesoderm

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Primary Germ Layers
Figure 7.14. Formation of the three primary germ
layers.
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Germ Layers (contd.)
Figure 7.15. Organs derived from the germ
layers.
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Structures formed from the three germ layers.
Figure 7.16.
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Ectodermal placodes in a representative
vertebrate.
Figure 7.17.
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Extraembryonic Membranes
Figure 7.18. Extraembryonic membranes of cledoic
egg.
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Extraembryonic Membrane Formation in a Bird
Figure 7.19. Extraembryonic membranes.
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Principles of Embryology
Figure 7.20. Embryological development.