GANGLION AR GRAY MATTER. 219 



path, destruction of the medial geniculate breaks the auditory 

 path. 



The superior colliculi of the corpora quadrigemina (Figs. 

 65 and 68) represent the optic lobes of birds, fishes and reptiles. 

 They contain the center of optic reflexes. In being stratified, 

 they bear some resemblance to the lateral geniculate bodies. 

 They possess three white and two gray layers: (i) The stratum 

 zonale (stratum album superficiale) is a layer of white matter 

 on the surface. This invests the laminated stratum griseum, 

 which forms the deep part of the colliculus and comprises two 

 gray and two white layers: (2) The stratum griseum super- 

 ficiale is composed of small multipolar cells. (3) The stratum 

 album medium is a layer of fibers separating the small from the 

 large multipolar cells. (4) The large cells make up the stratum 

 griseum profundum, underneath which is another layer of fibers. 

 (5) The stratum album profundum. The fibers of the superficial, 

 middle and deep strata comprise, first, those that enter the collic- 

 ulus through the optic tract and radiation, through the superior 

 and a part of the lateral fillet, the striato-thalamic tract and the 

 spino-thalamic tract; and, second, those that take origin in the 

 colliculus and leave it through the brachium superius or the 

 anterior longitudinal bundle. Of the fibers originating in the 

 superior colliculus and running through the brachium superius 

 it is supposed that some go as far as the retina; probably others 

 enter the cortical fillet. 



The anterior longitudinal bundle is made up of efferent axones 

 of the cell-bodies in the superior colliculus. ,It crosses at once 

 through the dorsal tegmental decussation (Fig. 68) and descends 

 ventro-lateral to the opposite medial longitudinal bundle, to the 

 anterior columna of gray matter in the spinal cord. Its fibers 

 end largely in the nuclei of the third, fourth and sixth cerebral 

 nerves and in the cervical enlargement of the spinal cord; but 

 perhaps others enter the remaining nuclei of motor cerebral 

 nerves, and a few fibers of the tract have been traced as low as 

 the lumbar region. This bundle is the great optic reflex tract. 

 The fibers to the nuclei of the third, fourth and sixth cerebral 

 nerves bring about the reflex movements of the eyeball, contraction 



