228 A MANUAL OF ANA TOMY. 



but narrows as it extends posteriorly, forming the outer por- 

 tion of the floor of the body of the ventricle ; then it turns 

 downward into the descending horn, forming in this position 

 the outer portion of its roof; finally it terminates in the 

 amygdaloid nucleus, which is placed in the anterior part 

 of the roof of the descending horn. 



The large anterior portion in the anterior horn is the 

 head of the caudate nucleus ; its body corresponds to the 

 body of the ventricle itself, while the tail of the nucleus is 

 its slender prolongation into the descending horn. 



The nucleus thus describes almost a complete circle and 

 shows two cut surfaces in horizontal or vertical transverse 

 sections. 



The Lenticular Nucleus. Is the lower and outer 

 extraventricular portion of the corpus striatum. In 

 horizontal section it is biconvex in shape and faces inward 

 and outward ; in vertical-transverse section it is triangular 

 or wedge-shaped, with the base of the wedge abutting on 

 the central lobe ; in vertical anteroposterior sections its 

 outline is oval with its lower part reaching to the base of 

 the brain (at the anterior perforated space). 



The lenticular nucleus is separated from the caudate 

 nucleus by a sheet of white fibres the internal capsule 

 which bounds it on the inside. There is a similar sheet of 

 white fibres bounding the nucleus upon its external surface 

 called the external capsule. The two nuclei are not en- 

 tirely separated by the internal capsule, as will be seen on 

 study of a series of anteroposterior sections, but they be- 

 come continuous with each other around the anterior 

 margin of the internal capsule ; they are also connected by 

 numerous fibres which pass through the anterior limb of 

 the internal capsule. 



A vertical transverse section of the nucleus in fresh speci- 



