46 ATLAS OF NERVE CELLS 



THE CORPUS QUADRIGEMINUM ANTERIOR 



THE corpora quadrigemina are four small masses of gray matter lying above the crura 

 cerebri and behind the optic thalamus, and are the smallest of the basal ganglia. They are 

 made up of alternate layers of white and gray matter. They receive numerous bundles of 

 nerve fibres from various parts of the nervous system, and they send out numerous bun- 

 dles of nerve fibres to the cortex. The corpora quadrigemina posterior receive fibres from 

 the acoustic nerve and from the fillet. They send fibres outward to the temporal region of 

 the brain. 



The corpora quadrigemina anterior receive fibres from the optic nerve and from the 

 fillet, and send fibres upward to the occipital cortex of the brain. These ganglia, therefore, 

 are to be regarded as junctions in the passage of nervous impulses, where some impulses 

 are switched off to side tracks, while others pursue their course along the main line. 



Plate XXII. shows a transverse section through the right corpus quadrigeminum anterior, 

 its free surface being seen above, and the aqueduct of Sylvius being seen below to the left. 

 It will be seen that everywhere through this section there is a fine interlacing plexus of nerve 

 fibres. It is also evident that there are several concentric layers to be seen. 



1. There is a layer of glia cells, which are stained deeply in the plate. 



2. The layer of superficial white fibres. In the plate the deeper mass of these nerve 

 fibres only is stained, the surface portion not having taken the stain. The fibres making 

 up this layer come from the optic nerve, their cells of origin lying in the retina. They 

 terminate in the corpora quadrigemina anterior in fine brush-like expansions and free endings. 



3. The superficial gray matter. This forms the layer beneath the superficial white 

 matter. It is narrow toward the median line, but broader along the middle of the body. 

 It contains numerous cells, large in size, of various shapes, with extensive branches. These 

 cells are better shown in Plate XXIII. 



4. The deep layer of white fibres. Some of these are seen in the plate to have a 

 direction from the median line outward. The majority, however, pass in an antero-posterior 

 direction, and are cut across in this section. They radiate widely into the superficial gray 

 matter, and also enter the deeper gray matter. Many of these fibres are supposed to be 



