DISSECTING MANUAL. 



callosum; the caudate nucleus projects onto its floor. The 

 posterior horn curves backward and inward, tapering; the 

 callosal tapetum forms its roof and outer wall. On its inner 

 wall are two curved elevations, the upper (bulb of the cornu) 

 being formed by the forceps major, and the lower (calcar avis) 

 by the calcarine fissure. The ventricle is triangular (trigonum 

 ventriculi) in the angle between the diverging posterior and 

 descending horns. [573] 



The descending horn runs backward and outward, then 

 downward around the thalamus, and then forward almost to 

 the temporal pole. Its roof, formed chiefly by the tapetum, 

 presents prolongations of the taenia semicircularis and tail of 

 the caudate nucleus, and also at its tip a bulging (amygda- 

 loid tubercle) produced by the amygdaloid nucleus. The floor 

 presents internally a curved elevation (hippocampus major), 

 produced by the dentate fissure, which is narrowed behind, 

 thickened at its anterior end, and partly covered by the 

 choroid plexus; the fimbria is attached to its inner border. 

 A smooth elevation (eminentia collateralis} , produced by the 

 collateral fissure, lies in the trigonum ventriculi, and occasion- 

 ally another (eminentia collateralis anterior) , produced by the 

 anterior part of the collateral fissure, is seen external to the 

 hippocampus major. [576] 



An arched cleft (choroid fissure), which is normally closed 

 by a layer of ependyma attached to its margins, opens into 

 the whole body and descending horn between the fornix and 

 thalamus, and between the fimbria and roof. Through it the 

 choroid plexus, which is derived from the edge of the velum 

 interpositum, projects into the ventricle, invaginating the 

 ependyma. [578] 



Caudate Nucleus. This is an arched gray mass with a large 

 head which projects into the anterior horn of the lateral ven- 

 tricle, a narrower part which is seen on the floor of the body, 

 and a long thin tail which curves onto the roof of the descend- 

 ing horn to join the amygdaloid nucleus. Lenticular Nucleus. 



[44] 



