FUNCTIONS OF THE CEREBRUM. 531 



may, perhaps, be explained by assuming that the division 

 or injury of the crus cerebelli produces paralysis or 

 imperfect and disorderly movements of the opposite side 

 of the body ; the animal falls, and then, struggling with 

 the disordered side on the ground, and striving to rise with 

 the other, pushes itself over; and so, again and again, 

 with the same act, rotates itself. Such movements cease 

 when the other crus cerebelli is divided; but probably only 

 because the paralysis of the body is thus made almost 

 complete. 



'STRUCTURE AND PHYSIOLOGY or THE CEREBRUM. 



The cerebrum is placed in connection with the pons and 

 medulla oblongata by its two'crura or peduncles (fig. 149) : 

 it is connected with the cerebellum, by the processes called 

 superior crura of the cerebellum, or processus a cerebello ad 

 testes, and by a layer of grey matter, called the valve of 

 Vieussens, which lies between these processes, and extends 

 from the inferior vermiform process of the cerebellum to 

 the corpora quadrigemina of the cerebrum. These parts, 

 which thus connect the cerebrum with the other princi- 

 pal divisions of the cerebro-spinal nervous centre, form 

 parts of the walls of a cavity (the fourth ventricle) and a 

 canal (the iter a tertio ad guartum ventriculum) which are 

 the continuation of the canal that in the foetus extended 

 through the whole length of the spinal cord and brain. 

 They may, therefore, be regarded as the continuation of 

 the cerebro-spinal axis or column ; on which, as a develop- 

 ment from the simple type, the cerebellum is placed ; and, 

 on the further continuation of which, structures both larger 

 and more numerous are raised, to form the cerebrum 

 (fig. 142). 



The cerebral convolutions appear to be formed of nearly 

 parallel plates of fibres, the ends of which are turned 

 towards the surface of the brain, and are overlaid and 



M M 2 



