494 



THE HUMAN EMBRYO. 



the cervical region, at the junction of the head and trunk, the 



under surface of the head is still almost in contact with the tail. 



The several parts of the brain are readily distinguished 



BR.i 



HY 



SU 



MN 



LA 



VN 



LP 



FIG. 204. Human Embryo lettered by Professor His, A, and estimated as 

 twenty-seven days old. (From His.) x 13. 



BR.I, first branchial arch. El, auditory vesicle. HC.l, first branchial cleft. 

 HM, hyomandibular cleft. HY, hyoid arch. LA, fore-limb or arm. LP, hind-limb 

 or leg. MN", mandibular arch. MX, maxillary arch. OC, lens. OF, olfactory pit. 

 O J, Jacobson's organ. SIT, sinus prtecervicalis. VN, villi of chorion. 



through the skin, the mid-brain being especially prominent. 

 The nerve ganglia, both cranial and spinal, are well developed, 

 and form swellings that are clearly visible from the surface. 



The olfactory pits, OF, on the under surface of the fore part 



