CHAP, vi.] THE BRAIN, 641 



observers have obtained similar results in other animals ; and it has 

 in general been found that lateral or unsymraetrical lesions and 

 incisions produce a greater effect than those which are median or 

 symmetrical. Section of the middle peduncle on one side almost 

 invariably gives rise to a forced movement, the animal rolling 

 rapidly round its own longitudinal axis ; the rotation is generally 

 though not always towards the side operated on; and is accompanied 

 by nystagmus, i.e. by peculiar rolling movements of the eyes sug- 

 gestive of vertigo ; frequently one eye is moved in one direction, ex. 

 gr. inwards and downwards, and the other in a different or opposite 

 direction, ex. gr. outwards and upwards. As we have already said 

 the permanent effects which follow upon injury to the semicircular 

 canals, have been attributed by some to secondary mischief being 

 set up in the cerebellum. The clinical evidence is discordant, for 

 though unsteadiness of gait has been frequently witnessed in cases 

 of cerebellar disease, many histories have been recorded in which 

 extensive disease, amounting at times to almost complete destruc- 

 tion, of the cerebellum has existed without any obvious disturbance 

 of the coordination of movements. Still the experimental evidence 

 is so strong, that we must consider the cerebellum as an important 

 organ of coordination, though we are unable at present to define its 

 functions more exactly. 



In this connection we may observe that the history of the 

 developement of the spinal cord (see p. 600) tends to connect a 

 definite portion of the lateral columns of the spinal cord with the 

 cerebellum ; but the meaning of this connection is obscure. 



Attempts have been made to connect the cerebellum with the 

 sexual functions ; but there is no satisfactory evidence of any such 

 relation. As we shall see later on, the nervous centres connected 

 with the sexual and generative organs are seated, in the case of 

 dogs at least and probably of all animals, in the lumbar spinal cord; 

 and all or nearly all sexual phenomena may be witnessed in animals, 

 in which the lumbar spinal cord has been isolated by section 

 from the rest of the cerebro-spinal system. Galvanic stimulation 

 of the cerebellum produces no change in the generative organs, and 

 when erection of the penis is caused by emotions, the tract con- 

 necting the cerebral convolutions with the erection-centre in the 

 spinal cord must be supposed to pass straight along the crura cerebri 

 and medulla, for it has been observed that stimulation of these parts 

 in the dog will produce erection. 



Crura Cerebri and Pons Varolii. Though from the grey 

 matter abundant in both these organs we may infer that they 

 possess important functions, we hardly know more concerning 

 them than that the former serve as the great means of communi- 

 cation between the spinal cord and the higher parts of the brain, 

 and that both are intimately connected with the coordination of 

 movements, since either forced or disorderly movements are the 



F. 41 



