214 



STUDY OF PIG EMBRYOS. 



Md.obl. 



ascending lateral part of the pharynx is a portion of the first gill pouch or future 

 Eustachian tube, and is quite clearly marked off from the pharynx proper by 

 its oblique direction. Of the acustico-facial ganglion complex the section shows 

 four parts: the ganglion vestibuli, G. -yej-/; the geniculate ganglion, G. ^en; the 

 sensory root, Fac, of the facial nerve arisingrfrom the geniculate ganglion and 

 entering the brain to form there a distinct fiber-tract which is oval in the section 



and lies just below the entering vesti- 

 bular fibers, and is clearly indicated in 

 the drawing; and, finally, the motor 

 tract, t. m, of the facial nerve. This 

 tract is a very distinctly marked bun- 

 dle of nerve-fibers which arise from 

 neuroblasts of the ventral zone, tra- 

 verse that zone almost horizontally, 

 then bend downward and pass out from 

 the brain-wall, appearing as the lateral 

 root of the facial nerve. The root runs 

 first toward and then past the genicu- 

 late ganglion. The jugular vein, Jug, 

 lies outside of the ganglia ; not, as does 

 the earlier cardinal vein, inside. In the 

 mandible below the pharynx appear 

 two nerves. Of these, the upper is the 

 hypoglossal, A^. 12, which lies near the 

 angle formed by the jugular of the first 

 gill cleft with the pharynx. The lower 

 of the two nerves, Mx. i, is the inferior 

 maxillary. 



Section through the Otocyst. — The 

 figure is from a section not far from 

 the last. The hind-brain has narrowed 

 considerably; its thickened floor, Md. 

 obi, the anlage of the medulla oblon- 

 gata, rises steeply from the median line. Its ependymal roof, epen, is less 

 expanded than in figures 126 and 127. It forms a sharp angle in the dorsal 

 median line. The median ventral fissure between the two sides of the 

 medulla is deeper than further forward. The pharynx, Ph, is wide and has 

 expanded laterally into the common beginning of the first and second gill 

 pouches. Between the pharynx and the raphe the basilar artery, A. has, 



Fig. 127. — Pig, 12.0 mm. Frontal Series 6, 

 Section 380. 

 A.bas, Basilar artery. Coch, Cochlea. D.e, Ductus 

 endolymphaticus. epen, Ependyma. Fac. 711, 

 Motor division of the facial nerve. Jug, Jugu- 

 lar. Vl^.o^/, Medulla oblongata. /'/4, Pharynx. 

 raph, Median raphe of the medulla oblongata. 

 S.c, Anlage of the semicircular canals. Ve, Vein. 

 X 22 dianis. 



