940 



THE NERVE SYSTEM 



is reflected upon the invaginated choroid plexus of the lateral ventricle. The 

 choroid plexus of the middle cornu is more voluminous than that of the body 

 of the ventricle, and must be lifted in order to expose the whole of the ventricular 

 aspect of the hippocampus. 



At the apex of the middle cornu the roof presents a more or less pronounced 

 bulging, the amygdaloid tubercle, due to the presence of the amygdaline nucleus, 

 a small mass of ganglionic gray from which the taenia semicircularis arises and in 

 which the caudate nucleus apparently ends. 



The posterior cornu or postcornu is a shorter diverticulum which passes toward 

 the occipital pole in a gently curved course, with its convexity directed laterad. 

 It is not very capacious, usually slit-like on section, and tapers to a point within 

 2 or 3 cm. of the occipital pole. Its roof, slanting lateroventrad, is formed by the 



FIG. 692. Diagram showing the topography of the lateral ventricle, middle meningeal artery, and cerebrum 



within the cranium. 



tapetum of the corpus callosum. On the inner or mesal wall two elongated 

 bulgmgs may be observed. The upper or dorsal elevation, called the occipital 

 bulb or bulb of the cornu (bulbus cornu posterior is, callesal eminence [Wilder]), 

 is formed by the compact arched posterior forceps of the corpus callosum as it 

 curves around the very deep occipital fissure. The occipital bulb is not always 

 well marked. Ventrad of it lies a more constant limbus or welt-like elevation, 

 the calcar (calcar avis; hippocampus minor), a projection produced by the infolding 

 of the cerebral wall along the calcarine fissure. The choroid plexus does not 

 enter the posterior cornu. 



The choroid fissure or rima (rima transversa cerebri magna; fissure of Bichat) 

 is not a true fissure, and only becomes one when the choroid plexus of the lateral 

 ventricle is torn from its connections. The choroid fissure is nevertheless a gap 

 between the diencephalic part and the overlapping and recurved telencephalon 

 produced by the extension of the secondary fore-brain vesicles in an arcuate manner. 



