352 NERVOUS SYSTEM. 
another as they pass craniad, finally disappearing beneath the 
cerebral hemispheres. Each is made up of many fibre-bundles, 
which are apparent in surface view (Fig. 
142). The peduncles are separated by 
a small triangular space, which is marked 
by a median longitudinal sulcus. In this 
space, just caudad of the mammillary 
bodies, is a small area through which a 
number of blood-vessels pass into the 
brain. This is known as the posterior 
perforated area (or substance) (Fig. 
142, 7). The cerebral peduncles (a) are 
Fic. 142.VENTRAL Sur- Crossed by the tractus transversus pedun- 
ee pete lees cularis (4) (see above). 
WITH THE Pons. The third cranial nerve (Fig. 138, 
#, pedunculi cerebri; 4 777) (N. oculomotorius) leaves the brain 
tractus transversus peduncu- : 
laris; ¢, corpus geniculatum at the medial border of the cerebral 
Pein ate peduncle (g), just caudad of the tractus 
§; mammillary bodies; A transversus peduncularis. 
poe ene une tee The aqueductus cerebri (Fig. 143, 7; 
been removed); 7, posterior Fig. 153, @) (or aqueduct of Sylvius) is 
a ae won one fied, the continuation craniad of the fourth 
fifth, seventh, and eighth ventricle. It is a narrow passage, one 
cranial nerves. epi < F : 
or two millimeters in diameter, lying 
dorsad of the pedunculi cerebri and ventrad of the corpora 
quadrigemina. 
C. PROSENCEPHALON.—The prosencephalon or primitive 
forebrain includes the diencephalon or ‘tween-brain and the 
telencephalon or cerebral hemispheres. 
4. Diencephalon.—The diencephalon or ’tween-brain in- 
cludes the thalami and the other parts bounding the third 
ventricle. The diencephalon is seen in entire brains only in 
ventral view (Fig. 138, ¢, d, e, etc.) 
The diencephalon may be considered as forming almost or 
quite the most cranial portion of the median nervous tube,— 
the cranial wall of the third ventricle (the lamina terminalis) 
(Fig. 143, @), ending in the median line in the deep fissure 
between the hemispheres of the cerebrum. Parts of the brain 
