298 



STUDY OF PIG EMBRYOS. 



gata well outside the tractus solitarius, which, however, it joins just before the 

 spinal cord is reached. The other root of the nerve, L.R, is lateral. It lies below N 

 the ganglion near the median plane. Its fibers arise from neuroblasts in the ventral 

 zone and gather together as a distinct bundle which starts near the median line, 

 takes a curving course through the ventral zone, and makes its exit from the 



medullary wall at the dorsal limit of the 

 zone. It has a striking resemblance to the 

 root of the facial nerve. We do not yet 

 know whether such a course of the fibers 

 is characteristic of all lateral roots or only 

 of the trigeminal and facial roots. On the 

 medial side of the trigeminal ganglion is a 

 large vein, Card, the anterior cardinal vein. 

 In the median line in the mesenchyma 

 immediately below the raphe is the section 

 of the basilar artery, and considerably below 

 that is the small section of the notochord 

 which it is very difficult to distinguish with 

 a low power. Between the notochord and 

 the cardinal vein is the section of the 

 carotid artery. 



m Section through the Acustico-facial 

 FIG. 204. PIG, 12.0 MM. FRONTAL SERIES 6, Ganglion (Fig. 204). In this section the 



SECTION 340. 



A. has, Arteria basilaris. D.Z, Dorsal zone of the 

 medulla oblongata. EC, Ectoderm, epen, 

 Ependymal roof of the fourth ventricle. /, 



thickened ventral wall of the hind-brain 

 (i. e., the anlage of the medulla oblongata) 

 is not spread out nearly horizontally, as in 



N.I2, Hypoglossal nerve. PA, Pharynx, t.m, 

 Motor tract of facial nerve. X 22 diams. 



Median fissure of the medulla oblongata. Fac, the trigeminal region, but rises obliquely on 

 Sensory root of the facial nerve. G.gen, Gen- either side from the median line. The 



iculate ganglion of the facial nerve. G.vest, , . j i r, i r .1 j n 



. , , right and left sides of the medulla are 



Ganglion vestibuli of the acoustic nerve. Jug, 



Lateral vein, mes, Mesenchyma. Mx.i, In- divided from one another by a deep 



ferior maxillary branch of the trigeminal nerve. median fissure, /. In the median line WC 



see also the basilar artery, A.bas, and 

 still lower the wide, slit-like pharynx, Ph, 

 the outer portion of which ascends obliquely toward the lateral vein, Jug. The 

 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.vest; the geniculate ganglion, G.gen; the sensory 

 root, Fac, of the facial nerve arising from 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 vestibular fibers, and is clearly indicated in the drawing; 

 and, finally, the motor tract, t.m, of the facial nerve. This tract is a very dis- 



