35 2 



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 

 FIG. 142. VENTRAL SUR- crossed by the tractus transversus pedun- 



FACE OF THE MlDBRAIN cu l aris (b\ (sCC above). 

 AND ' fWEEN-BRAIN, \ J \ 



WITH THE PONS. The third cranial nerve (Fig. 1 38,, 



a. pedunculi cerebri; 6, ///) (J$ m OCUlOHlOtorius) leaves the brain 

 tractus transversus peduncu- 1-111 



laris; c, corpus geniculatum at the medial border of the cerebral 

 mediate; </, optic tract; e, pe d u ncle (g-}, just caudad of the tractus 



optic chiasma ;/, optic nerve ; * 



g, mammillary bodies; h, transversus peduilCularis. 



;;Sh"! The aqueductus cerebri (Fig. ,43, /; 



been removed);/', posterior Fig. 153, d~) (or aqueduct of Sylvius) is 

 perforated area; k. pons. ,1 ,- , j r 0.1 r ^.1 



III V VII VIII. third t " e continuation craniad of the fourth 

 fifth, seventh, and eighth ventricle. It is a narrow passage, one 



cranial nerves. .... . ,. 



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, c, 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, d}, ending in the median line in the deep fissure 

 between the hemispheres of the cerebrum. Parts of the brain 



