462 PHYSIOLOGY 



and especially with the complex mechanism we have already studied 

 in connection with the labyrinth and cerebellum. Stimulation of 

 the corpora quadrigemina therefore evokes movements of the eyes 

 and of the head ; extirpation of this part, though it may interfere 

 with co-ordination, does not necessarily involve loss of sight, even 

 when the extirpation is bilateral. 



The multifarious intercourse which is continually taking place 

 between the eye centres and those for the movements of the body ; 

 and between afferent impressions from the eyes and those from the 

 semicircular canals and the proprioceptive system generally, is 

 effected to a large extent through the intermediation of the posterior 

 longitudinal bundle, which extends throughout the whole length 

 of the mid-brain and the hind-brain, and in the spinal cord becomes 

 continuous with the anterior basis bundle of the anterior columns. 

 Receiving fibres above through the anterior commissure from the 

 optic thalamus, and from the superior corpora quadrigeminal bodies, 

 it is associated in its course with the three motor nuclei that give 

 origin to the nerves supplying the muscles of the eyeball, viz. the 

 third, fourth, and sixth nerves. Fibres enter the posterior longi- 

 tudinal bundle from the auditory system, from the facial nucleus, 

 and from the superior olive, and connections are also established 

 between this bundle and the nucleus of Deiters, representing the 

 central station of impulses from the labyrinth. The general con- 

 nections of the bundle are shown in Fig. 205. 



