Laboratory Workbook in Developmental Anatomy

Laboratory Exercise 16
Learning Objectives
 To recognize a chick embryo at this stage of development.
 To identify the structures that have developed at this stage of embryonic
development.

INTRODUCTION
The developmental changes which have taken place in a 96-hour chick embryo
generally involved the growth in size of the structure. Apparently, the length of the embryo
at this incubation period is not markedly greater than that of the 72-hour stage because of
the cranial cervical and caudal plexus. The main divisions of the body such as the head,
trunks and tail are now clearly defined and the appendage, allantois and very large vitelline
vessels can easily be located.
1. Flexion – progressed in the cranial, cervical, dorsal and caudal regions of the body
resulting in the bending of the embryo on its self and the head and tail lie close
together
2. Torsion –is now complete so that the entire body of the embryo now lies with its
left side on the yolk
3. Branchial arches – now very thick making the aortic arch traversing them very
difficult to see
4. Telencephalon – large and almost touches the allantois
5. Olfactory pit – faces the apex of the ventricle
6. Allantois – enlarged and projected as a stalked vesicle from the hind gut region
7. Appendage buds – relatively increased in size
8. Ventricle – now lying between the telencephalon and the liver prominence
9. Omphalomesentric veins and arteries – close together, entering and leaving the
body at the level of the midgut. The veins are anterior to the artery.
10. Somites – now extend from the region of the myelencephalon to the tail.

MATERIALS
 Compound microscope
 Prepared slides

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ACTIVITY
Examine a whole mount of a 96-hour chick embryo with the lowest magnification
possible, draw and label the part. Don’t forget your color code for the germ layers
derivative/s of the parts of the embryo.

Whole mount of a 96-hour chick embryo

Most of the structures seen in this incubation period of the chick embryo has been
identified in the 72-hour chick embryo. The structures to be encountered in this exercise
are grouped according to their germ layer derivatives.

Ectodermal Derivatives
1. Skin (epidermis)
2. Oral cavity (stomodaeum)
3. Nasal cavity (olfactory pit)
4. Lens
5. Cloaca (proctodaeum)
6. External auditory vesicle
7. Telencephalon
8. Diencephalon
9. Mesencephalon – include the optic cup, lens, epiphysis and infundibulum
10. Metencephalon and diencephalon

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Endodermal Derivatives
From the endoderm of the foregut
1. Pre-oral gut
2. Pharynx
3. Thyroid gland
4. Laryngotracheal groove
5. Esophagus
6. Lung bud
7. Stomach
8. Liver
9. Pancreas – derived from a single median dorsal and 2 (pair) ventro-lateral
pancreatic buds. The dorsal origin appears at about 72 hours while the ventro-
lateral pancreas appears toward the end of the 96 hours. The common duct which
connects the liver and the ventral pancreas to the duodenum is called ductus
choleductus.

Mesodermal Derivatives
1. Mesenchyme
2. Dorsal mesoderm
a. Myotome – gives rise to the skeletal muscles
b. Dermatome – gives rise to the dermis of the skin & other connective tissues
c. Sclerotome – gives rise to the axial skeleton

3. Lateral mesoderm
a. Somatic mesoderm
b. Splanchnic mesoderm
c. Coelom (intraembryonic & extraembryonic)
4. Intermediate mesoderm
a. Mesonephric duct and tubules
b. Metanephric duct
5. Branchial arches
6. Maxillary process
7. Arteries and veins
8. Heart

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The Extra-embryonic Membranes

1. Amnion – innermost membrane enclosing the embryo. It is derived from the
somatopleure and consists of 2 layers: inner ectoderm layer and outer somatic
mesoderm layer.
2. Serosa or chorion – covers the dorsal surface (right side away from the yolk) of the
chick embryo. It is also derived from the somatopleure and consists of an inner
layer of somatic mesoderm and an outer layer of ectoderm.
3. Yolk sac – separates the embryo from the underlying yolk. It is derived from the
outer splanchnopleure and consists of an inner ectoderm (of the midgut) and an
outer splanchnic mesoderm which presents numerous blood vessels. The yolk sac
covers the ventral surface of the embryo and joins the serosa on either side (lateral
side) of the embryo
4. Allantois – a bladder-like structure that arises from the ventral wall (floor) of the
hind gut. It is derived from the splanchnopleure and consists of an inner entoderm
(of the hind gut) and an outer splanchnic mesoderm.

Examine the serial transverse sections of a 96-hour chick embryo passing through
the level of the stomach, telencephalon, allantois and lungs.

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_____________________________________________________

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STUDY QUESTIONS

1. Describe the shape of the embryo at this incubation period. How the embryo acquire
such shape?
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2. How many pairs of somites do you see in a 96-hour chick embryo?
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3. Name prominent difference/s you noticed between 72 and 96 hours.
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Laboratory Exercise 17
Learning Objectives
 To recognize a pig embryo at this stage of development.
 To identify the parts or structures of a 6-mm pig embryo.

INTRODUCTION
The 6 mm pig embryo is actually on the 18th day of the gestation period.
Fundamental similarities of this embryo to the early chick already studied is apparent. The
fetal membranes of the pig are somewhat intermediate between the chick and man. The
amnion, chorion, and allantois develop very prominently as in the chick. The yolk sac is
small and rudimentary, so its functions are transferred to the allantois which fuses with
the chorion; the two constitute the placenta which is the organ of fetal respiration,
nutrition, and excretion.

MATERIALS
 Compound microscope
 Prepared slides

ACTIVITY
Examine a whole mount of a 6-mm pig embryo under 4X magnification, draw and
label. The structures of the pig embryo at this stage correspond to those of the 96-hr chick
embryo. Like the whole mount of the 96-hr chick embryo, 6mm pig embryo is shaped like
a letter C.
The extra-embryonic membranes (amnion, serosa and allantois) develop in the
same manner as in the chick but their functions are modified.

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Whole mount of a 6-mm pig embryo

Examine the serial transverse sections of 6-mm pig embryo, draw and label. The
following are significant developmental features which are non - existent in the 96-hr chick
embryo:
1. Copula
2. Tuberculum impar
3. Lateral lingual primordia
4. Mandibular process
5. Pharyngeal pouch 2
6. Pharyngeal pouch 3
7. Maxillary process

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Transverse section taken at the level of the tongue

Transverse section taken at the level of the liver

Transverse section taken at the level of the ventricle

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Transverse section taken at the level of the atrium

Transverse section taken at the level of the mesonephros

STUDY QUESTION

1. Provide the adult structures that arise from the following primordia:
a. Copula
______________________________
b. Tuberculum impar
______________________________
c. Lateral lingual primordia
______________________________

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d. Mandibular process
______________________________
e. Pharyngeal pouch 2
______________________________
f. Pharyngeal pouch 3
______________________________
g. Maxillary process
______________________________

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