656 THE NERVOUS SYSTEM. 



which is connected with the tuber cinereum through the intervention of a thin 

 layer of gray substance, the lamina cinerea. This may be exposed by gently 

 raising and drawing back the optic commissure. A white band may be observed 

 on each side, passing backward from the under surface of the corpus callosum, 

 across the posterior margin of the anterior perforated space to the hippocampal 

 gyrus, where each meets the corresponding outer root of the olfactory tract : these 

 bands are called the peduncles of the corpus callosum. They may be traced 

 upward around the genu to become continuous with the striae longitudinales on its 

 upper surface. Laterally, this portion of the corpus callosum extends into the 

 frontal lobe. 



The lamina cinerea is a thin layer of gray substance, extending backward from 

 the termination of the corpus callosum above the optic commissure to the tuber 

 cinereum ; it is continuous on each side with the gray matter of the anterior per- 

 forated space, and forms the anterior part of the inferior boundary of the third 

 ventricle. 



The optic commissure is situated in the middle line, immediately in front of the 

 tuber cinereum and below the lamina cinerea ; that is to say, the commissure is 

 superficial to the lamina in the order of dissection when the base is uppermost. It 

 is the point of junction between the two optic tracts, and will be described with 

 the cranial nerves. Immediately behind the diverging optic tracts, and between 

 them and the peduncles of the cerebrum (crura cerebri), is a lozenge-shaped 

 interval, the inter peduncular space, which is bounded behind by the pons Varolii, 

 and in which are found the following parts : the tuber cinereum, infundibulum. 

 pituitary body, corpora albicantia, and the posterior perforated space. 



The tuber cinereum is an eminence of gray matter, situated between the optic 

 tracts, and extending from the corpora albicantia to the optic commissure, to which 

 it is attached ; it is connected with the surrounding parts of the cerebrum, forms 

 part of the floor of the third ventricle, and is continuous with the gray substance 

 in that cavity. From the middle of its under surface a conical tubular process of 

 gray matter, about two lines in length, is continued downward and forward to be 

 attached to the posterior lobe of the pituitary body. This is the infundibulum, 

 and its canal, which is funnel-shaped, communicates with the third ventricle. 



The pituitary body (hypophysis cerebri] is a small, reddish-gray, vascular mass, 

 weighing from five to ten grains, and of an oval form, situated in the sella turcica, 

 where it is retained by a process of dura mater, named the diaphragma sellae. 

 This process covers in the sella turcica, and has a small hole in its centre through 

 which the infundibulum passes. 



Structure. The pituitary body is very vascular, and consists of two lobes, 

 separated from one another by a fibrous lamina. Of these, the anterior is the 

 larger, of an oblong form, and somewhat concave behind, where it receives the 

 posterior lobe, which is round. The two lobes differ both in development and 

 structure. The anterior lobe, of a dark, reddish-brown color, is developed from 

 the epiblast of the buccal cavity, and resembles to a considerable extent, in micro- 

 scopic structure, the thyroid body. It consists of a number of isolated vesicles 

 and slightly convoluted tubules, lined by epithelium and united together by a very 

 vascular connective tissue. The epithelium is columnar and occasionally ciliated. 

 The alveoli sometimes contain a colloid material, similar to that found in the 

 thyroid body, and their walls are surrounded by a close network of lymphatic and 

 capillary blood-vessels. The posterior lobe is developed as an outgrowth from the 

 embryonic brain, and during foetal life contains a cavity which communicates 

 through the infundibulum with the cavity of the third ventricle. In the adult it 

 becomes firmer and more solid, and consists of a sponge-like connective tissue 

 arranged in the form of reticulating bundles, between which are branched cells, 

 some of them containing pigment. In the lower animals the two lobes are quite 

 distinct, and it is only in the mammalia that they become fused together. 



The corpora albicantia or mammillaria are two small, round, white masses, 

 each about the size of a pea, placed side by side immediately behind the tuber 



