412 CEREBRUM. 



at the pons, but becoming more transverse as they ascend to 

 the optic thalami, and corpora striata ; here they become en- 

 larged and flattened, and enter these latter bodies. As they 

 ascend from the pons they diverge, and are connected by the 

 intercrural lamina, or middle perforated plate. The optic 

 tracts pass over them internally and in front, and they form 

 the floor of the iter a tertio ad quartum ventriculum. Each 

 crus is marked by a groove into two tracts, one of which is 

 continuous with the anterior pyramidal tract through the 

 pons, on to the corpus striatum the other, which is the 

 larger, corresponds to the olivary body and goes to the thal- 

 amus. On cutting the crus it presents, near its centre, a 

 mass of gray matter having rather a darkish appearance, 

 and called locus niger. On the inner surface of the crura 

 is seen the attachment of the third pair of nerves. The 

 size of the crura, it is believed, bears a proportion to that 

 of the hemispheres into which they expand. 



The Corpora mammillaria, or albicantia, (Fig. 16,) are two 

 small white bodies, about the size of a pea, situated upon 

 the inner surfaces of the crura at their anterior extremity. 

 Their structure is white externally, and gray or cineritious 

 within. Their relation is with the anterior pillars of the 

 fornix which terminate in them. They have the tuber 

 cinereum in front, and partly assist in closing the third 

 ventricle. These with the locus niger, are regarded as 

 ganglionic. 



The Tuber Cinereum (also calle&pons Tarini) is a soft, gray 

 body, on the under surface of the crura cerebri, in front of 

 the albicantia, and behind the optic commissures. It forms 

 the floor of the third ventricle. 



The Infundibulum is a conical tubular body of gray mat- 

 ter, proceeding from the centre of the tuber cinereum, and 

 descending to the pituitary gland in the sella turcica. Its 

 upper part opens into the third ventricle its lower part 

 forms the apex, and by some is said to be closed though 

 Meckel asserts it is open through its whole extent. 



The Pituitary gland is situated in the sella turcica of the 

 sphenoid bone, between the dura mater and tunica arach- 



