678 



THE CENTRAL AXIS OF THE NERVOUS SYSTEM. 



fissure the inter peduncular, which bifurcates in front to circumscribe the 

 mammillary or pisiform tubercle (corpus albicans, bulbi fornicis) (Fig. 327, 

 18) : a small, single, and rounded elevation of a white colour, like the 

 peduncles, covered by the pituitary gland, whose root is represented by the 

 tuber cinereum, and is situated in front of this body. 



Behind, the crura cerebri are limited by the anterior border of the pons 

 Varolii. In front, they are circumscribed by the optic nerves, which pass 

 obliquely around their anterior extremity and join on the middle line before 

 the tuber cinereum, to form a commissure called the cliiasma of the optic 

 nerves (Fig. 322, 7). On the sides, their tissue is confounded with that of the 



corpora quadrigemina and thalami 

 optici, which are superposed on the 

 cerebral peduncles. It may be 

 remarked that the part of their 

 lateral face situated below the 

 tubercula testes, forms a well- 

 defined triangular space, designated 

 the band ofReil, lateral triangular 

 fasciculus, and lateral oblique fasci- 

 culus of the isthmus. 



4. The Crura Cerebelli. 



The cerebellum is attached to 

 the upper face of the isthmus by 

 two short and thick lateral funiculi 

 of white substance, between which 

 is comprised the posterior ventricle ; 

 these constitute the cerebellar crura. 



Three distinct fasciculi enter 

 into the composition of each of 

 these cords : an anterior, a posterior, 

 and a middle. 



The latter, or middle cerebellar 

 peduncle (crus cerebelli ad pontem), 

 is the largest of the three. It is 

 formed by the prolongation of the 

 extremities of the pons Varolii 

 (Figs. 323, 2 ; 324, 6). 



The posterior cerebellar peduncle 

 (cms ad medullam oblongatum), the 

 most slender, is formed by the 

 restiform body, one portion of which 

 is reflected below the posterior root 

 of the auditory nerve to reach the 

 substance of the cerebellum. It 

 is closely united to the preceding, 

 from which it is with difficulty dis- 

 tinguished (Fig. 323, 3). 



The anterior cerebellar peduncle 

 (processus e cerebello ad testes) is a 

 fasciculus very distinct from the 

 to the middle peduncle, which it 



SUPERIOR VIEW OF THE ENCEPHALIC ISTHMUS < 



1, 1, Corpora restiformia ; 2, Section of the middle 

 cerebellar peduncles ; 3, Section of the posterior 

 cerebellar peduncle; 4, Anterior cerebellar 

 peduncle ; 5, Floor of the posterior ventricle ; 

 6, Valve of Vieussens; 7, 7, Tubercula testes; 

 8, 8, Tubercula nates; 9, 9, Thalami optici; 

 10, Corpus geniculatum internum ; 11, Corpus 

 geniculatum externum ; 12, Corpus striatum ; 

 13, Tsenia semicircularis ; 14, Pineal gland ; 

 15, Its peduncle ; 16, Common anterior open- 

 ing ; 17, 17, Anterior pillars of the trigonal ; 

 18, Trifacial nerve; 19, Facial nerve; 20, 

 Auditory nerve ; 21, Glosso-pharyngeal nerve ; 

 22, Pneumogastric nerve ; 23, Spinal nerve. 



other two, related by its inner border 



