CORPUS QUADRIGEMINUM ANTERIOR 47 



derived from the occipital cortex, being the termination of axis cylinders which arise from 

 the cells there. Others come from, or pass to, the optic thalamus, many crossing the median 

 line in the posterior commissure. 



5. The deep gray matter forming the innermost layer is made up of numerous nerve 

 cells small in size. These do not appear to have any direct communication with the 

 visual apparatus, but are in connection with the fibres of the lateral fillet and of the red 

 nucleus. 



6. The gray matter surrounding the aqueduct of Sylvius has a homogeneous appearance 

 like that surrounding the central canal of the spinal cord, the so-called gelatinous substance 

 of Rolando, and is made up chiefly of neuroglia. 



Von Monakow 1 has shown that when the optic nerve is divided, the superficial white 

 layer and the superficial gray layer undergo atrophy. He has also shown that when the 

 occipital cortex is extirpated, the deep white matter undergoes atrophy, and the superficial 

 gray matter is also slightly affected. Hence, he believes that the visual tract consists of 

 two segments, each of which has a double system of fibres. The first segment extends from 

 the retina to the corpus quadrigeminum anterior (also to the corpus geniculatum externum 

 and optic thalamus). Many of the fibres in this segment arise from cells in the retina, 

 and terminate in a fine network in the corpus quadrigeminum. Others, much fewer in 

 number, arise from the cells in the corpus quadrigeminum and terminate in the retina. The 

 second segment extends from the corpus quadrigeminum (corpus geniculatum externum and thala- 

 mus) to the occipital cortex. Many of the fibres in this segment arise from the cells of the corpus 

 quadrigeminum and terminate in a brush-like expansion in the occipital cortex. Others arise from 

 the pyramid cells of the cortex, and terminate in free extremities about cells of the corpus quadri- 

 geminum. The facts established by the investigation of degenerations after lesions, either experi- 

 mentally produced in animals or found in man, support this arrangement of double tracts, not 

 only in the visual apparatus, but also in the auditory apparatus, and in fact in all the sensory 

 tracts. Hence they must be accepted as proven. A similar arrangement is present in all the 

 tracts entering and leaving the optic thalamus, as will be seen when this ganglion is studied. 

 In the diagram (Fig. 8) these double tracts with their respective origins and terminations 

 are shown. 



The function of the anterior corpora quadrigemina is to coordinate the visual impulses which 

 result in ocular movements whether automatic or voluntary. When it is remembered that the 

 eyes will follow a light either automatically during unconsciousness, or voluntarily because of an 

 act of attention, it becomes evident that a double tract, one from the retina, the other from the 



1 C. von Monakow, Archiv f. Psychiatric, Bd. XX. s. 714. 



