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 
