356 NERVOUS SYSTEM* 



medullary matter seems to be much more considerable ; and the 

 arbor vita? arrangement is proved to depend upon the laminae 

 of medullary matter radiating from the centre, or, in other 

 words, from the massive medullary trunk in the interior of the 

 hemisphere of the cerebellum. Each of these radiations com- 

 mences by a root of considerable size, which divides and sub- 

 divides into branches. Each primitive radiation, as well as its 

 branches, is covered by its own layer of cineritious matter 

 about one line in thickness, ^nd is kept perfectly distinct from 

 the contiguous ones by the fissures which extend internally 

 from the periphery of the cerebellum. 



In the middle of the trunk of the arbor vitae, exists the Cor- 

 pus Rhomboideum, or Dentatum. It is an oblong rounded body, 

 jagged and cineritious in its circumference, but medullary with- 

 in. Its configuration resembles that of the corresponding body 

 in the eminentia olivaris, with the addition of its being larger, 

 and having its outline better marked. It is the ganglion of the 

 cerebellum of Gall and Spurzheinru 



The Valve of Vieussens (Velum Medullare, Valvula Cerelri) 

 arises from the cerebellum, just under the anterior part of the 

 base of the monticulus, and runs obliquely upwards to terminate 

 in the testes. Sometimes it is marked in its middle, by a lon- 

 gitudinal line or slight fissure, from either side of which pro- 

 ceed small lateral ones. It is principally medullary, and has a 

 small quantity of cineritious matter at its extremities. It is 

 thinner in the middle than at either of its margins. 



The Central or Fundamental Portion of the Cerebellum ex- 

 hibits also very clearly the arborescent arrangement, and is fur- 

 nished with about seven primitive radiations, coming from a 

 medullary trunk. The proportion; of medullary matter to corti- 

 cal, is less in it than in the hemispheres of the cerebellum. 

 Each of the primitive radiations may be traced to some particu- 

 lar point or prominence on the surface of the fundamental por- 

 tion, thus forming its basis; but this study is more curious than 

 useful, though several anatomists have pursued it. 



Three medullary fasciculi, on each side, have now been 

 traced to the cerebellum ; one of these is the continuation of the 

 corpus restiforme of the medulla oblongata; a second is the val- 

 vula cerebri ; and the third, the Crus Cerebelli, which joins the 

 annular protuberance. The two first fasciculi belong to the 



