INTERNAL STRUCTURE OF THE PONS 149 



which are continuous with the fibrse pontis. There are also some small nerve- 

 cells of Golgi's Type II, the short axons of which end in the adjacent gray mat- 

 ter. Within these nuclei terminate the fibers of the corticopontine tracts and 

 some collaterals from the corticospinal fibers. Collaterals from the medial 

 lemniscus are also found arborizing in those nuclei of the pons which lie im- 

 mediately ventral to that bundle. This gray matter, therefore, represents an 

 important association apparatus within which there terminate fibers from 

 several different sources. 



From what has been said it will be apparent that the pons serves to estab- 

 lish an important and for the most part crossed connection between the cere- 

 bral hemispheres and the cerebellum, a cortico-ponto-cerebellar path. The cor- 

 ticopontine fibers take origin from pyramidal cells in the frontal and temporal 

 lobes and end in the nuclei pontis. Arising from the cells in these nuclei, most 

 of the transverse fibers cross the median plane and reach the opposite cerebellar 

 hemisphere through the brachium pontis (Fig. 106). 



THE DORSAL OR TEGMENTAL PART OF THE PONS 



The dorsal or tegmental part of the pons (pars dorsalis pontis) resembles in 

 structure the medulla oblongata (Fig. 108). On its dorsal surface there is a 

 thick layer of gray matter which lines the rhomboid fossa. Between this layer 

 and the basilar portion of the pons is the reticular formation divided by the 

 median raphe into two symmetric halves. This has essentially the same struc- 

 ture here as in the medulla oblongata, and contains the continuation of many 

 longitudinal tracts with which we are already familiar. The restiform body at first 

 occupies a position similar to that which it has in the medulla, along the lateral 

 border of the rhomboid fossa; but it soon bends dorsally into the cerebellum. 



The Cochlear Nuclei. At the point of transition between the medulla and 

 pons the restiform body is partly encircled on its lateral aspect by a mass of 

 gray matter formed by the terminal nuclei of the cochlear division of the acoustic 

 nerve (Fig. 107). There may be distinguished a dorsal and a -ventral cochlear 

 nucleus at the dorsal and ventral borders of the restiform body. Within these 

 nuclei the fibers of the cochlear nerve end; while those of the vestibular nerve 

 plunge into the substance of the pons ventromedially to the restiform body to 

 reach the floor of the fourth ventricle (Fig. 134). Fibers from the dorsal cochlear 

 nucleus run medially upon the floor of the fourth ventricle in the striae medullares 

 (Fig. 89), and sinking into the tegmentum join the fibers from the ventral coch- 

 lear nucleus in the trapezoid body. 



