THE BRAIN. 501 



It is in this locality that hemorrhage produces such serious 

 consequences. The blood-vessels supplying the basal ganglia 

 may rupture on account of a diseased condition, and as a result of 

 this apoplexy or paralysis may occur, or the hemorrhage may prove 

 fatal. When the hemorrhage takes place into the anterior portion 

 of the internal capsule, hemiplegia, or paralysis of motion in the 

 opposite side of the body, will -result ; while if it is into the poste- 

 rior part, paralysis of sensation will occur on the opposite side. 



Optic Thalami (Fig. 290). Each of. these bodies is covered 

 by a layer of white fibers, which is especially prominent in the 

 internal capsule. From the capsule it enters the thalamus, con- 

 necting it with the hemisphere. The gray matter of the thalamus, 

 of which it is principally composed, is aggregated into two masses, 

 an outer and an inner nucleus, separated by a white lamina, the 

 internal medullary lamina. In the anterior portion there is a third 

 portion of gray matter, in which the nerve-cells are quite large. 

 The cells of the thalamus are multipolar and fusiform. 



Corpora Quadrigemina. These bodies, 4 in number, the ante- 

 rior pair being the testes, and the posterior the nates, are situated 

 behind the third ventricle and posterior commissure and under 

 the posterior border of the corpus callosum. They consist 

 principally of gray matter. Each gives off a bundle of white 

 fibers to the corpora geniculata, which joins the optic tract of 

 the same side, and each receives fibers of the fillet which can be 

 traced to nuclei of the opposite funiculus gracilis and cuneatus. 

 Thus the fillet serves as a channel for afferent impulses which 

 have traversed the fibers of the posterior roots of the spinal 

 nerves. These nerves arborize around the cells of the nuclei, 

 from which the fibers of the fillet arise. Over the gray matter of 

 the superior corpora quadrigemina is a layer of nerve-fibers which 

 have their origin in the nerve-cells of the retina, coming by way 

 of the optic tract, and which pass into the corpora quadrigemina 

 and arborize around the cells of the gray matter. Schafer says 

 that these cells "are very various in form and size, and are dis- 

 posed in several layers, which are better seen in the optic lobe of 

 the bird (Fig. 292) than in mammals. Most of their processes 

 pass ventralward. Their destination is not certainly known, but 

 some appear to pass downward with the fillet, others probably 

 turn upward and run in the tegmentum toward the higher parts 

 of the brain ; while others, perhaps most, probably form terminal 

 arborizations around the motor cells of the oculomotor and other 

 motor nuclei. All the nerve-fibers of the optic nerve and optic 

 tract do not enter the corpora quadrigemina. Some pass into the 

 lateral geniculate bodies and form arborizations there. On the 

 other hand, from the cells of these geniculate bodies the axis- 

 cylinder processes appear to pass to the cortex of the brain 

 (occipital region)." 



