FUNCTIONS OF THE BKAIN. 821 



striati, the caudate and lenticular nuclei, and the corpora quadrigemina 

 being connected with the medulla by means of the cerebral peduncles 

 above which are situated the corpora quadrigemina. 



In the domestic animals the anterior pair of the corpora quadri- 

 gemina are composed of gray matter, while the posterior are white in 

 direct opposition to what is the case in man. In herbivora and in the 

 hog the anterior pair are the larger, while in carnivora they are of equal; 

 size, or the posterior may be somewhat more developed. Between the 

 corpora quadrigemina and the optic thalamus lies the third ventricle, 

 while under the corpora quadrigemina is situated the aqueduct of 

 Sylvius, connecting the third and fourth ventricle. 



We have now to attempt an explanation of the functions of these 

 different parts of the brain. 



3. The Pons Varolii. — We have seen that the pons, the superior 

 continuation of the spinal cord, is composed of two sets of fibres. The 

 one, the transverse fibres, constituting the median cerebellar peduncles, 

 serves to connect the two lateral hemispheres of the cerebellum and exists 

 only in animals in which the cerebellum consists of two lobes. The other 

 part of the pons is composed of a mass of gray substance in continuity 

 with that of the medulla and traversed in an antero-posterior direction 

 by the fibres of the medulla, passing up to form the cerebral peduncles. 



As in the study of other portions of the nervous system, we attempt 

 here to determine the functions of the different parts of the brain by the 

 method of excitation and excision. 



When the pons is stimulated, either mechanically or by an electric 

 current, pain and muscular spasms are produced, evidently by the mere 

 implication of adjacent motor and sensory paths. Where section of the 

 pons is performed there may be sensory, motor, or vaso-motor paralysis, 

 together with forced movements when the middle cerebellar peduncles 

 are involved. Thus, if there be an injury to the lower half of one side 

 of the pons there will be both sensory and motor paralysis of the face 

 on the same side and more or less general paralysis of the opposite side 

 of the body; if the injury be to the upper half of the pons the facial 

 paralysis will be on the same side as the paralysis of the bod}'. 



The pons, like the spinal cord and medulla, also acts as a reflex 

 centre; although this fact is not capable of direct demonstration, its 

 truth is rendered probable by the higher degree of muscular co-ordination 

 preserved by an animal in which the pons has been retained over animals 

 in whom the section has been carried through the brain below this point. 



4. The Cerebral Peduncles. — The cerebral peduncles form the 

 upward prolongation of the pons, and are constituted by those portions 

 of the spinal cord which, after having traversed the pons and medulla, 

 pass upward through the optic thalamus and corpora striata to enter the 



