220 THE CEREBRUM. 



of the pupil and accommodation to distance; while those fibers 

 which end in the gray substance of the lower part of the cervical 

 enlargement of the spinal cord, called the cilio-spinal center, 

 through the white rami communicantes and cervical sympathetic, 

 produce dilatation of the pupil. The latter constitute the pupillo- 

 dilator tract. 



Destructive lesions affecting the superior quadrigeminal collic- 

 uli produce loss of reflex movement of the eyeballs, loss of pupillary 

 reflex and loss of accommodation. 



The inferior colliculi of the corpora quadrigemina form 

 a relay in the auditory path (Figs. 65 and 69). They are made 

 up of a white stratum zonale, whose fibers are continuous chiefly 

 with the lateral fillet and brachium inferius, and of a deep gray 

 mass, the nucleus colliculi iuferioris, which is composed of small 

 multipolar cell-bodies in a network of fibers. The nuclei of the 

 two eminences fuse in the median plane. In the nuclei end a 

 considerable number of fibers belonging to both lateral fillets, 

 but most of them belong to that of the same side; and from them 

 proceed axones of the auditory paths through the brachia inferiora 

 to the medial geniculate bodies. A few fibers of the spino-thala- 

 mic tract also end in the inferior colliculus. Again this colliculus 

 receives a small bundle of the striato-thalamic fibers and, probably, 

 corticifugal fibers of the temporo-thalamic radiation. 



Though the greater part of the lateral fillet passes by the 

 inferior colliculus without relay, a lesion in this body is apt to 

 involve the entire bundle and cause almost complete deafness 

 in the opposite ear. 



Nucleus Lateralis Superior (Fig. 68). In the reticular for- 

 mation of the tegmentum at the level of the superior quadrigeminal 

 colliculus is the nucleus lateralis superior. It contains large 

 multipolar cell-bodies. The nucleus forms a relay both for 

 ascending and descending fibers of the formatio reticularis. 

 According to Tschermak, a small fasciculus runs from this nucleus 

 into the medial longitudinal bundle where it divides T-like; and 

 its descending fibers run down through the anterior fasciculus 

 proprius of the cord (Barker). The spino-thalamic tract prob- 

 ably undergoes a partial relay in the superior lateral nucleus. 



