384 



BASE OF THE BRAIN. 



Fig. 172* 



which communicates with the cavity of the third ventricle ; and below the 

 termination of the canal, the conical process becomes connected with the 

 pituitary gland. The infundibulum and tuber cinereum form part of the 

 floor of the third ventricle. 



The Pituitary gland (hypophysis cerebri), is a small, flattened, reddish- 

 grey body situated in the sella turcica, and closely retained in that situation 

 by the dura mater and arachnoid. It consists of two lobes, closely pressed 

 together, the anterior lobe being the larger of the two, and oblong in shape, 

 the posterior round. Both lobes are connected with the infundibulum, 

 but the latter is so soft in texture as to be generally torn through in the 

 removal of the brain. Indeed, for the purposes of the student, it is better 

 to effect this separation with the knife, and leave the pituitary body in situ, 

 to be examined with the base of the cranium. 



The Corpora albicantia (mammillaria, pisiformia, bulbi fornicis) are two 

 white convex bodies, having the shape and size of peas, situated behind 

 the tuber cinereum, and between the crura cerebri. They are a part of 

 the crura of the fornix, which, after their origin from the thalami optici, 

 descend to the base of the brain, and making a sudden curve upon them- 

 selves previously to their ascent to the lateral ventricles, constitute the cor- 

 pora albicantia. When divided by section, these bodies will be found to 

 be composed of a capsule of white substance, containing grey matter, the 

 grey matter of the two corpora being connected by means of a commissure. 



The Locus perforatus is a layer 

 of whitish-grey substance, connect- 

 ed in front with the corpora albi- 

 cantia, behind with the pons Varo- 

 lii, and on each side with the crura 

 cerebri, between which it is situated. 

 It is perforated by several thick tufts 

 of arteries, which are distributed 

 to the thalami optici and third ven- 

 tricle, of which latter it assists in 

 forming the floor. It is sometimes 

 called the pons Tarini. 



The Crura cerebri are two thick 

 white cords, which issue from the 

 anterior border of the pons Varolii, 

 and diverge to each side to enter 

 the thalami optici. By their outer 

 side the crura cerebri are continu- 

 ous with the corpora quadrigemina, 

 and, above, they constitute the 

 lower boundary of the aqueduct of 



* The under surface or base of the brain. 1. The anterior lobe of one hemisphere 

 of the cerebrum. 2. The middle lobe. 3. The posterior lobe almost concealed by (4) 

 the hemisphere of the cerebellum. 5. The pyramidal lobe of the inferior vermiform 

 process of the cerebellum. 6. The pneumogastric lobule. 7. The longitudinal fissure. 

 8. The olfactory nerves, with their bulbous expansions. 9. The substantia perforata at 

 the inner termination of the fissure of Sylvius; the three roots of the olfactory nerve are 

 seen upon the substantia perforata. The commencement of the transverse fissure on 

 each side is concealed by the inner border of the middle lobe. 10. The commissure of 

 The optic nerves ; the numeral is placed between the optic nerves as they diverge from 

 the commissure, and rests upon the lamina cinerea of the corpus callosum. 11. The 



