Comparative Anatomy of Vertebrates Chapter 5 Early Craniate Morphogenesis

1. Comparative
Anatomy
Of the
Vertebrates
Larry J. Sultiz
Presented to:
Prof. Gloria
Galan

2. CHAPTE
R
5

3. Early Craniate
Morphogenesis

4. All craniates pass
through similar, though
not identical, early
formative stages.

5. Eggs are microlecithal,
mesolecithal or macrolecithal,
depending on the quantity of
the yolk.
They are isolecithal or
telolecithal, depending on the

6.  Microlecithal – very little yolk (e.g.
placental mammal)
 Mesolecithal – moderate amounts of
yolk (e.g. amphibians)
 Macrolecithal – massive amounts of yolk
(e.g. reptiles, birds)
 Isolecithal – yolk is evenly distributed
 Telolecithal – cytoplasm and yolk tend to
accumulate

7. Oviparity is the condition in
which unfertilized or fertilized
egg are shed to the exterior for
development and hatching.
Oviparous – animals that spawn or

8. Viviparity is a condition in
which offspring are born alive.
The developing organism may
or may not be dependent on
the parent for nourishment
before birth.Viviparous – animals that retain their
eggs within the mother’s body during

9. Viviparity is found in some
members of every craniate
class except agnathans and
birds.

10. Euviviparity is a viviparous
condition in which offspring are
dependent on the parent for
nourishment throughout
pregnancy.Histotrophic nutrition – nutrition by
glandular secretions from maternal tissues

11. Ovoviviparity viviparous
condition in which offspring are
not dependent on the parent
for nourishment throughout
pregnancy.

12. Fertilization is internal in
viviparous species, in urodeles
and apodans, and in species
that cover egg with a shell.

13. Cleavage follows fertilization. It produces a
blastula with a blastocel.
•Holoblastic cleavage occurs when the cleavage
furrows pass through the entire egg
•• cleavage can either be equal, where the
resulting cells contain the same amount of
yolk, or unequal, in which some cells contain
more yolk than others:
• - equal cleavage occurs in microlecithal
eggs
• - unequal cleavage occurs in
mesolecithal eggs

14. •Meroblastic cleavage occurs more in
macrolecithal eggs
• cleavage takes place only in a disk at
the animal pole
• the cleavage furrows do not extend into
the yolk
• results in the formation of the

17. Gastrulation
Characterized by cell movement
and reorganization within the
embryo (morphogenetic
movements) to the interior of the
embryo, forming three primary
germ layers:

18. .

19. In therian mammals, an inner
cell mass gives rise to the
embryo.
Gastrulation is by
delamination or a
modification thereof.

20. A trophoblast membrane
develops from the blastula wall,
providing initial embryo and
uterine contact.

21. Neurulation results in formation of a brain or
spinal cord.

22. Organoge
nesis
•After the production of the nerve
tube, differentiation of the germ
layers occurs rapidly, and
organogenesis begins, in which the
primary tissues differentiate into
specific organs and tissues

23. Morphogen are inductor
(signaling) proteins that induce
organization of the germ layers
and participate in
differentiation of specialized
tissues from embryonic
mesenchyme.

24. Mesenchyme is an embryonic
tissue consisting of
undifferentiated, totipotent,
embryonic cells that
require inductor
factors for
differentiation.

25. Ectoderm contributes epidermis
and its derivatives, the entire
nervous system, epithelia of special
sense organs such as lateral eyes
and inner ears, and lens of paired
eyes, the lining of the stomodeum
and proctodeum, and a broad
spectrum of miscellaneous tissues

26. Neural crest give rise to the
sensory ganglia on the roots of the
cranial and spinal
nerves, to autonomic ganglia,
to many of the skeletal
components of the skull and
pharyngeal arches, to most
pigment cells, and to numerous

27. Ectodermal placodes give rise to
neurosensory cells of the olfactory
epithelium, to sensory epithelia of
the inner ear, to a variety of
mechanoreceptive and
electroreceptive organs of fishes,
and to some neuroblasts in the
ganglia of the cranial nerves VII,

28. Endoderm gives rise to the
epithelium of the digestive tract
and to the epithelioid components
of the organs that evaginate from
it.

29. Dorsal mesoderm forms
mesodermal somites consisting of
sclerotome , dermatome and
myotome.
These give rise, respectively, to
vertebrae and the ribs, the dermis
of the dorsum and skeletal muscles

31. Lateral-plate mesoderm splits into
somatic and splanchnic layers.

32. The somatopleure consists of
somatic mesoderm plus ectoderm.
The splanchnopleure consists of
splanchnic mesoderm plus
endoderm.

33. The coelom is the cavity between
the somatic and splanchnic
mesoderm. It is initially segmented
in cephalochordates.

34. Intermediate mesoderm gives rise
to kidney tubules and to the ducts
of the urogenital system.

35. The chief extraembryonic
membranes are yolk sac, amnion,
chorion, and allantois.