CRANIAL CAVITY. 



This is a gray mass lying external to the caudate nucleus 

 but directly continuous with it below. Two vertical white 

 laminae (external and internal medullary) divide it into three 

 zones, of which the outer is the putamen, while the two inner 

 form the globus pallidus. The caudate and lenticular nuclei 

 form the corpus striatum. [579] 



Claustrum. This is a thin gray lamina in the white matter, 

 between the lenticular nucleus and cortex of the island of 

 Reil. The taenia semicircularis is a band arising mostly from 

 the amygdaloid nucleus. Running backward on the roof of 

 the descending horn it then curves forward on the floor of the 

 body of the lateral ventricle, just internal to the caudate nu- 

 cleus ; then running through the foramen of Monro it descends 

 both in front of and behind the anterior commissure to the 

 locus perforatus anticus. [582] 



The external capsule is a thin white lamina between the 

 putamen and claustrum; it joins the internal capsule in front. 

 The internal capsule is a broad white band directly contin- 

 uous with the crusta of the eras cerebri below, but radiating 

 (corona radiata) to the cortex above. It separates the len- 

 ticular nucleus from the thalamus, tsenia semicircularis, and 

 caudate nucleus, and is bent on itself opposite the tsenia semi- 

 circularis, with the angle (genu) directed inward. The portion 

 (about one-third) in front of the genu is the anterior limb; the 

 remainder is the posterior limb. [583] 



NERVES. 



Exit of Cranial Nerves. The olfactory arise from the bulb 

 and descend through the cribriform plate. The optic tracts 

 unite, over the optic groove, in the optic chiasm, from which 

 the optic nerve runs on each side through the dura and the 

 optic foramen. The oculo-motor pierces the dura between the 

 free arid attached borders of the tentorium, runs uppermost 

 in the outer wall of the cavernous sinus, and divides in the 

 sphenoidal fissure into upper and lower branches. The trochlear 



[45] 



