THE ANATOMY OF A SIX MM. PIG EMBRYO 



93 



the tail shorter. The cervical flexure is more marked, the olfactory pits 

 larger and deeper. The liver is more prominent than in the 6 mm. pig, 

 the mesonephros and segments less so. 



\fyelencephalon 



Metence photon 



A' .n* js^ x * jitua fe^ i "mi IJH 



Spinal cord 



Cervical segment S 



Future milk line 



Mesencephalon 



Diencephalon 



Yolk sac and 

 umbilical cord 



Thorack segment 12 



Lumbar segment 5 



FIG. 94. A human embryo 7 mm. long, viewed from the right side (Mall in Kollmann). 

 X 14. /, //, ///, Branchial arches I, 2, and 3; H, Ht, heart; L, liver; L', otic vesicle; R, ol- 

 factory placode; Tr, semilunar ganglion of trigeminal nerve. 



DISSECTIONS OF THE VISCERA 



To understand the sectional anatomy of an embryo, a study of dissec- 

 tions and reconstructions is essential. For methods of dissection see p. 

 139, Chapter 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. 95 shows the central nervous system and 

 viscera exposed on the right side of a 5.5 mm. embryo. The ventro-lateral 

 wall of the head has been left intact, together with the lens cavity, ol- 

 factory pit, and portions of the maxillary and mandibular processes, 

 second and third branchial arches, and cervical sinus (cf. Fig. 93). The 

 brain is differentiated into the five regions: telencephalon, diencephalon, 



