LATERAL DISSECTION OF THE VISCERA 



99 



The cervical flexure is more marked, the olfactory pits larger and deeper. The 

 liver is more prominent, the mesonephros and segments less so than in the 

 6 mm. pig. 



Lateral Dissection of the Viscera 

 To understand the sectional anatomy of an embryo, a study of dissections 

 and reconstructions is essential. For methods of dissection see p. 146, Chapter 



Spinal cord 



Cervical seg 



Myelenccphaloa 



^% -^telencephalon 



yf— Mesencephalon 



— Diencephalon 



Yolk-sac and 

 umbilical cord 



Thoraci-c seg- 

 ment 12 



Lumbar segment 5 



F IG gn. — A human embryo 7 mm. long, viewed from the right side (Mall in Kallmann's Hand- 

 atlas). I, II, III, branchial arches 1, 2 and 3; H, III, heart; L, liver; V, otic vesicle; R, olfactory 

 placode; Tr, semi-lunar ganglion of trigeminal nerve. 



VI. Before studying sections, the student should become as well acquainted 

 as possible with the anatomy of the embryo and compare each section with the 

 figures of reconstructions and dissections. 



Nervous System. — Fig. 90 shows the central nervous system and viscera 

 exposed on the right side of a 5.5 mm. embryo. The ventrolateral wall of the 

 head has been left intact with the lens cavity, olfactory pit, and portions of the 

 maxillary and mandibular processes, second and third branchial arches and 



