THE CEREBRUM. 363 



stance of the crus reaches the posterior inferior part of the cor- 

 pus striatum, and is immediately invested in the greater part of 

 its circumference with cineritious matter, it then begins to ex- 

 pand after the manner of a fan into filaments. These filarn/ents 

 or fasciculi penetrate the cineritious matter in various direc- 

 tions, besides those just detailed. A particular exposition of 

 them is given by Gall and Spurzheim, in their anatomy of the 

 brain. 



The Tsenia Striata is placed in the angle formed between the 

 internal margin of the Corpus Striatum, and the external one 

 of the Thalamus Opticus, where these two bodies are in con- 

 tact and continuous with one another. It is a small medullary 

 band, not a line in breadth, commencing near the anterior crus 

 of the fornix, with which it is connected frequently by filaments ; 

 and observing the curved course of th fissure in which it is 

 placed, it goes to the posterior end of the corpus striatum, and 

 even beyond it in most cases, by uniting itself to the lop of the 

 Cornu Ammonis. 



The Corpus Callosum. When the fissure between the he- 

 mispheres of the cerebrum is widely separated, or when the su- 

 perior part of the hemisphere is cut away on a level with the 

 bottom of the fissure, the Corpus Callosum, a medullary layer, 

 as stated, is brought fully into view. This body unites the me- 

 dullary mass of the two hemispheres, and is a large commis- 

 sure. It occupies about two-fifths of the long diameter of the 

 brain, being nearer to its anterior than to its posterior end, and 

 is about eight lines broad; increasing, however, somewhat in 

 breadth posteriorly. The lateral half of it, on either side, is 

 concealed by the hemisphere overlapping it, but is prevented 

 from adhering by a horizontal fissure, which extends from one 

 end to the other. It has an arched form, being convex above 

 and concave below. Its thickness is uniformly about three lines, 

 with the exception of its anterior and its posterior margins, 

 which are more. Just above the horizontal fissure there exists 

 a longitudinal layer of white neurine running from one end to 

 the other of the flat surface of the hemisphere, described by 

 Mr. Solly.* 



* Anatomy of Brain, 1836. 



