ANATOMY AND PHYSIOLOGY OF THE BRAIN. 417 



which cross each other at right angles. These are the 

 corpora quadrigemina. These are larger in the lower 

 animals than in man ; the two anterior are largest in soli- 

 peds and ruminants, and the two posterior in carnivora. 

 On each side of the corpora quadrigemina are two grey 

 bodies bent upon themselves (corpora geniculata), which, 

 with the former and the optic thalami, give origin to the 

 corresponding nerves of sight. From the posterior part 

 of the corpora quadrigemina two considerable white pro- 

 cesses pass upward and backward into the little brain, of 

 which they constitute the anterior peduncles. Stretched 

 across between these peduncles, and above the anterior part 

 of the fourth ventricle, is a white expansion containing also 

 grey stride, and known as the valve of Vieussens. In this 

 valve may be noticed the fibres of origin of the fourth 

 cranial nerve. 



The little brain or cerebellum lies above the medulla and 

 behind the brain. It is of considerable size in our domestic 

 animals, and consists of two lateral lobes joined in the 

 median line by an elongated worm-like eminence (vermi- 

 form process). The whole surface is covered by rugae, with 

 intervening depressions, in which the external grey matter 

 dips deeply into its substance. The great depth of these 

 grey folds gives to the central white substance an arbores- 

 cent appearance, from which it takes the name of Tree of 

 Life (arbor vitse). In the substance of each hemisphere is 

 a grey nodule indented at its edges, the dentated body of 

 the cerebellum. This body contains ramifying white layers 

 internally. 



The white substance of the cerebellum is connected to 

 adjacent parts by six prolongations of its substance, arranged 

 in pairs, and known as its peduncles. The anterior peduncles 

 pass downward and forward to join the corpora quadri- 



VOL. ii. 3 x 



