368 NERVOUS SYSTEM. 



rebrum, and by paring ofTthe vermis superior cerebelli. Though 

 the name implies four distinct prominences, yet they are formed 

 from a common mass of nine or ten lines square, on the poste- 

 rior surface of which these prominences arise. They are in 

 pairs, and are separated from one another by a crucial depres- 

 sion. The largest, or upper pair, is the Nates, the lower pair 

 the Testes. The external surface of these bodies is medullary, 

 and within they are cineritiqus. From the Nates there pro- 

 ceeds a considerable medullary fasciculus, which runs forward 

 to join the Corpus Geniculatum Internum on the internal pos- 

 terior face of the lhalamus nervi optici; there proceeds also 

 from them a second fasciculus, which either joins the optic 

 nerve itself, or the contiguous part of its thalamus. The Testes 

 receive, at their lower end, the valve of the brain; and there 

 also proceeds from them a large fasciculus of medullary matter, 

 which joins the Corpus Geniculatum Externum of the optic 

 thalamus. 



Of the Ventricles of the Brain. 



These cavities are four in number: two, called lateral, are 

 placed one in either hemisphere of the cerebrum, a third is be- 

 tween the two thalami, and the fourth under the cerebellum. 

 They have all been alluded to, but only incidentally. 



The two Lateral Ventricles (Ventriculi Laterales) are hori- 

 zontal cavities, or fissures, of an extremely irregular shape, in 

 the very centre of the hemispheres, being the interval between 

 the diverging and converging filaments of the cerebrum. They 

 are separated from each other only by the septum lucidum; are 

 covered over by the corpus callosum, and have the fornix, tha- 

 lami optici, and corpora striata for a floor. Each one consists 

 in a body or principal cavity, and three processes, called cor- 

 nua. The body has been sufficiently described in speaking of 

 the parts which constitute its parietes; but the processes are 

 yet to be considered. 



The Corrrua, from their position, are named Anterior, Poste- 

 rior, and Lateral or Inferior. The Anterior is a very small 

 space between the anterior extremity of the corpus striatum 

 and the opposite surface of the hemisphere, and has nothing in 



