THE ENCEPHALON. 425 



others should not be injured, they may be influenced by the 

 extension of the irritation from the injury f , and by sympathy 

 with the injured parts; just, for example, as we see epilepsy 

 from exciting causes in every part of the encephalon and from 

 exciting causes even in distant organs ; amaurosis is frequently 

 induced by wounds of the supra-orbital nerve, sometimes by 

 wounds of the infra-orbital nerve, and of the portio dura; M. 

 Fleurens declares that, in cutting the semicircular canals in which 

 the acoustic nerves only are spread, peculiar motions occurred. 

 If the horizontal canal on each side was divided, horizontal 

 movement of the head took place from side to side, and rotation 

 of the whole body. Division of the inferior vertical canals on 

 each side produced vertical movements of the head, and caused 

 the animal to lie on its back. Division of the superior vertical 

 canals caused vertical movements of the head, but the animal lay 

 forwards. The direction of the inferior vertical canal is back- 

 wards, and of the superior forwards. If all the canals were 

 divided, all sorts of violent motions took place. h Some parts 

 which have distinct names are only portions of organs, so that 

 injury of several parts may have the same effect; we may 

 have blindness from wounding the optic nerves, the tractus 

 optici, or the corpora quadrigemina. Some parts which have 

 distinct names are compound, so that the immediate and obvious 

 effect of injuring them is not the only consequence which would 

 be observed if the others had an opportunity of becoming appa- 

 rent. The chorda oblongata is an instance of this 1 , and all the 

 double nerves of sensation and motion. k 



f See Gall, 1. c. 8vo. t. iii. p. 409. sqq., where examples are given. 



B See many cases in Mr. Wardrop's work, On the Morbid Anatomy of the Eye, 

 vol. ii. p. 179. sqq. The fact is even mentioned by Hippocrates; and, what is 

 singular, the blindness generally arises from an imperfect division of the nerve, 

 and has been cured by making the division complete. The blindness has some- 

 times taken place instantly, sometimes come on very gradually. 



h M6m. de VAcad. des Sc. t. ix. p. 454. sqq. 



1 " The tubercula quadrigemina are a continuation of the bands of the me- 

 dulla oblongata and medulla spinalis. They are also formed by ganglia, one 

 portion of which gives origin to the fibres of the optic nerve. 



" In the same manner, the medulla oblongata is in a great measure a continu- 

 ation of the spinal marrow, besides containing many collections of non-fibrous 

 substances, which, like so many ganglions, are the origins of many nerves of 

 the highest importance, and relating to very different functions. 



