CHAP. X.] PITUITARY BODY VENTRICLES OF THE BRAIN. 289 



mingle or interlace with them in some intricate way, so that they 

 may come into intimate or frequent contact ? Or, do they, like 

 other fibres, blend with the gray matter, and thus connect the 

 really dynamic portion of the segments ? This latter view seems 

 to be the most probable. 



The pituitary body or hypophysis is a glandiform mass lodged in 

 the sella Turcica, and surrounded by the coronary sinus. It is 

 connected with the brain by the infundibular process, the small 

 extremity of which is attached to its superior concave surface. 



This body consists of two lobes, of which the anterior is much 

 the larger ; and which also differ in point of colour, the anterior 

 being of a yellowish gray, the posterior more similar to the gray 

 matter of the brain. The former is considerably denser and firmer 

 than the latter, which does not differ in consistence from the cere- 

 bral gray matter. The infundibulum is chiefly connected with the 

 posterior lobe. 



In point of structure, this body resembles somewhat the vesicular 

 matter of the brain. We find in it large vesicles with distinct 

 nuclei and nucleoli lodged in a granular matrix, and between them 

 numerous bundles of white fibrous tissue. These are most nume- 

 rous in the anterior lobe. Its use is quite unknown. 



Of the Ventricles of the Brain. By the apposition of the two 

 hemispheres of the brain along the median plane, a fissure-like 

 space is enclosed beneath the corpus callosum and foruix, limited 

 in front by the anterior pillars of the latter, and behind by the 

 posterior commissure ; this is the middle or third ventricle. This 

 fissure is closed inferiorly by the pons Tarini, mamillary tubercles, 

 and tuber cinereum ; its roof is formed by the velum interpositum, a 

 process of pia mater, which separates it from the body of the fornix. 

 It communicates posteriorly with the fourth ventricle through the 

 aqueduct of Sylvius (iter a tertio ad quartum ventriculum) 3 and imme- 

 diately behind the anterior pillars of the fornix it freely opens into 

 each lateral ventricle. At the same situation, the velum interposi- 

 tum and the choroid plexuses communicate with each other. The 

 optic thalami form the lateral boundaries of the third ventricle, 

 and its cavity is crossed by the soft commissure. 



The lateral ventricles result from the folding of the convoluted 

 surface inwards and downwards. By their extension inwards, and 

 tlu-ir junction along the median line by the corpus callosum, the 

 horizontal portion of each ventricle is enclosed ; and by the folding 

 inwards of the inferior convolutions, posterior to the fissure of 

 Sylvius, the inferior horn is formed. The horizontal portion 



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