THE SUBTHALAMIC REGION, ETC. 109 



We have now reviewed the origin of the optic nerve as shown in dissections 

 of the adult human brain. According to J. Stilling, there is added still another 

 root which ascends in the pedunculus cerebri from the medulla oblongata. 

 However, all these fibres and nuclei are so difficult to locate and follow out in the 

 human being that we must ask ourselves the question how far these discoveries 

 are borne out by investigations on the lower animals. Comparative anatomy 

 furnishes us an opportunity to study optic tracts of such a comparatively huge 

 size (in fishes and birds) that the relations of these parts can be much more 

 e;iMly determined. From the study of these animals, as well as of reptiles and 

 amphibians, we can see that the optic nerve, as a whole, certainly originates in 

 the anterior quadrigeminal body ; that in its course past the lateral geuiculate 

 body it receives fibres from that ganglion ; and that, finally, a basal root from the 

 region behind the infundibulum is associated with it. Experimental researches 

 on mammals (Gudden, Ganser, Monakow) show that the early extirpation of an 

 eye is followed by degeneration of the anterior qnadrigeminal body, of the corpus 

 geniculatum laterale, and of fibres from the pulvinar. The pulvinar is, however, 

 very small in most mammals, and first attains a considerable size in the primates. 



AVe may regard it as definitely settled that the optic nerve 

 has its origin in the anterior quadrigeminal body, the corpus 

 geniculatum lateralc, the pulvinar, the stratum zonale, and the 

 base of the brain. The roots from the corpus geniculatnm 

 mediale, the corpus subthalamicum, and the pedunculus cerebri 

 have not received the necessary corroboration by the various 

 methods of investigation. 



The connections between the cortex of the occipital lobe 

 and some of the points of origin of the optic nerve have already 

 been discovered. These connecting fibres make up the optic 

 radiation, which passes from the occipital lobe to the most 

 posterior part of the internal capsule, and from this point can 

 be traced into the thalamus and the brachium of the anterior 

 quadrigeminal body. It is shown in Fig. 44. Its fibres, how- 

 ever, do not end as there represented, in the lateral portions of 

 the occipital lobe, but trending toward the median line, in planes 

 which lie outside of this section, extend as far as the cuneus. 

 In destructive disease of the occipital lobe and of the posterior 

 part of the internal capsule the same symptoms appear as in 

 similar lesions of the optic tract on the same side. The outer 

 half of the retina of the eye on the injured side and the inner 

 half of the retina of the opposite eye degenerate. 



