THE CRANIAL NERVES AND THEIR NUCLEI 



175 



ventricular floor (Figs. 110, 121, 122). The fibers, which take their origin here, 

 are collected in the motor root or portio minor of the fifth nerve and run with its 

 mandibular division to the muscles of mastication. Within the nucleus there 

 terminate fibers from the corticobulbar tract and many fibers, chiefly collaterals, 

 from the central sensory tract of the trigeminal nerve. It also receives collat- 

 erals from the mesencephalic root of the trigeminal and from other sources 

 (Fig. 131). 



The motor nucleus of the facial nerve is located in the ventrolateral part 

 of the reticular formation of the pons near its caudal border (Figs. 108, 121, 

 122). Its constituent cells are arranged so as to form a varying number of sub- 

 groups which may possibly be concerned with the innervation of individual facial 

 muscles. 



Root of facial nerve, first part 

 Abducens nucleus 



Root of facial nerve, genu 



Root of facial nerve, second part 

 Facial nucleus 



Nucleus of abducens nerve 



Root filaments of abducens nerve 

 Stalk of superior olive 



Root of facial nerve, first part 

 Spinal root and nucleus N. V 

 Nucleus of facial nerve 

 Root of facial n., sec. 

 Superior olive [part 



Abducens nerve 



Fig. 124. Diagram of the root of the facial nerve, shown as if exposed by dissection in a thick 



section of the pons. 



From the dorsal aspect of this nucleus there emerge a large number of fine 

 bundles of fibers, directed dorsomedially through the reticular formation. These 

 rather widely separated bundles constitute the first part of the root of the facial 

 nerve (Fig. 124). Beneath the floor of the fourth ventricle the fibers turn sharply 

 rostrad and are assembled into a compact strand of longitudinal fibers, often 

 called the ascending part of the facial nerve. This ascends along the medial side 

 of the abducens nucleus dorsal to the medial longitudinal bundle for a consid- 

 erable distance (5 mm.). The nerve then turns sharply lateralward over the 

 dorsal surface of the nucleus of the abducens nerve, and helps to form the eleva- 

 tion in the rhomboid fossa, known as the facial colliculus. This bend around 

 the abducens nucleus, including the ascending part of the facial nerve, is known 



