The Nervous System 133 



said above, passes, as is usually the case, without 

 any line of demarcation into the spinal cord, the 

 obex filling in the apex of the fourth ventricle at the 

 anterior end of the median dorsal fissure. 



A lateral view of the brain is shown in Figure 

 30, C. The hemisphere, VH, is conical in outline, 

 with a small projection from the posteroventral 

 region; its continuation forwards as the olfactory 

 tract, Tro., and bulb, B. ol., is plain. Beneath it 

 and extending forwards are the prominent optic 

 nerve, II, and tract. Caudad to the latter and 

 projecting ventrad and caudad are the infundibu- 

 lum, Inf., and hypophysis, Hyp. 



Caudad to the cerebrum are seen the end of the 

 paraphysis, G.p., the optic lobes, MH, and the 

 cerebellum, HH. From the cerebral peduncles 

 (ventrad to the optic lobes) arises the oculomotor 

 nerve, III, and dorsocaudad to this, between 

 the optic lobe and the cerebellum, arises the 

 trochlear nerve, IV. From the middle zone (in a 

 dorsoventral direction) of the medulla, ventrad to 

 the cerebellum, arises the very large trigeminal 

 nerve, V; while from its usual place, on the ventral 

 surface of the medulla, the abducens nerve, VI, 

 takes its origin by several roots. At some dis- 

 tance caudad from the trigeminal, from the dorsal 

 surface of the medulla, as noted above, the very 

 large acoustic nerve, VIII, arises; and immediately 

 ventrad to this, on the side of the medulla, the 

 facial nerve, VII, may be seen. Commencing just 



