THE ISTHMUS. 773 



white bands, which commence at the base of the pineal gland, and are directed 

 forward parallel to each other, in the bottom of the fissure of the thalami optici, 

 to which they firmly adhere. On arriving; at the anterior common ojxining, they 

 become attached to the anterior pillare of the crura of the fornix. Sometimes 

 they are very narrow, and separated by an interval ; but more frequently they are 

 relatively wide, and immediately in contact on the median line. 



The conarium is far from always offering the same volume ; it has been 

 shown in its usual dimensions in Fig. 425, and in Fig. 429 it is shown as 

 incomparably larger. 



The tissue of the pineal gland is greyish in colour, and contains more or less 

 numerous calcareous granules. In the midst of its connective tissue are vesicles 



Fig. 426. 



LATERAL VIEW OF THE ISTHMUS. 



1, Medulla oblongata; 2, corpus rectiforme ; 3, lateral fasciculi of the medulla oblongata ; 4, inferior 

 fasciculus, or corpus pyramidale; 5, pons Varolii; 6, middle peduncle of the cerebellum; 7, 

 cerebral peduncle (crus cerebri); 8, testis; 9, natis ; 10, corpus geniculatum internum; 11, 

 corpus geniculatum e.xternum; 12, optic nerve; 13, fourth nerve resting on the band of Reil ; 

 14, sensitive root of the trigeminal nerve; 15, its motor root; 16, facial nerve; 17, auditory 

 nerve. 



filled with polyhedral cells ; it is in the centre of these vesicles that are found — in 

 old animals — mineral concretions (brain sand — acervuhis cerebri). Many anatomists 

 consider this body a vascular gland ; while others regard it as a nervous organ, 

 which has relations with the brain through the medium of its anterior peduncles. 



9. Pituitary Gland (Figs. 424, 11 ; 429, 19). 



The pituitcnj (/] a )i(/ — also named iha hypophysis cei'ebri aiid supra-sphenoidal 

 appendage — is a small disc-shaped tubercle, fixed to the anterior extremity of 

 the interpeduncular fissure by the pituitary stem (itifundibulum) and the tuber 

 cinereum. 



a. The tuber cinereum is a little eminence of a grey colour, situated in the 

 middle line, between the corpus albicans and the chiasma of the optic nerves, at 

 the anterior limit of the isthmus. This eminence is hollow, and its cavity is 

 nothing more than a diverticulum of the middle ventricle. 



