560 Dynamic Theory. 



visible in the ventricle of the hemisphere. It is the smaller tapering- 

 end and is called the nucleus caudatus or intra-ventricular ganglion. The 

 anterior end of the corpus striatum lies outside of the ventricle under 

 the hemisphere of the cerebrum. It is rounding and bulging toward 

 the latero-anterior part. It is the principal part and as regards motor 

 function the final part of the striatum. It is called the nucleus lenticu- 

 laris, or extra ventricular ganglion. Whatever motor connections the 

 nucleus caudatus possesses, they are by way of the lenticularis. The 

 latter has its direct connections with the foot of the crus ( motor ) and 

 with the tegmentum (sensory). Outside of the anterior parts of the cor- 

 pus striatum, viz. , the nucleus lenticularis, is a thin plate of gray mat- 

 ter called the claustrum, and outside of this and lying within the fissure 

 of sylvius is a lobule of convoluted gray matter called by various names, 

 as the Lobule of the Corpus Striatum, the Intermediate Lobule, the 

 Lobule of the fissure of Sylvius, and the Insula or Island of Reil. This 

 lobule and the adjoining convolutions of the cerebrum on the margin, 

 of the fissure of sylvius, are concerned in the faculty of motor speech. 

 The Island of Reil cannot be seen from the outside of the brain. 



It is now desirable to go back and describe other organs connected 

 with the medulla oblongata, and other parts of the encephalic isthmus. 



The Cerebellum. This is a large mass which lies on top of the fourth 

 ventricle, and in man constitutes -| to | of the whole brain. In man and 

 the mammals it consists of three lobes. The middle one, which is 

 called the vermis, occupies the cavity of the fourth ventricle. In the 

 lower animals, the vermis is much more prominent than in man, and in 

 birds it constitutes almost the whole of the cerebellum. It resembles 

 the dorsal view of a silk worm rolled up, with its extremities concealed 

 beneath. The middle part of the vermis is, in the higher animals, 

 broken up and ill defined, but the front and rear are easily seen, and 

 are called, respectively, the anterior and posterior vermiform process. 

 To the anterior vermiform process is attached the posterior border of 

 the valve of vieussens, or valve of the brain, which forms the frou* 

 boundary of the fourth ventricle and the hind boundary of the aque- 

 duct of sylvius. The posterior vermiform process is attached to the 

 restiform bodies by a membrane of triangular shape, which covers the 

 hind end of the fourth ventricle. The lateral lobes of the cerebellum 

 are like two halves of an irregularly-shaped sphere. They are covered 

 with sulci and fissures running in many windings, and penetrating to 

 various depths into their substance. Unlike the medulla oblongata and 

 spinal cord, the gray vesicular matter of the cerebellum is on the out- 

 side. It is in two layers, separated by a thin layer of white matter. 

 Both layers contain nerve cells and other small, rounded bodies, the 

 whole constituting the cortex. This cortex covers the convolutions, and 



