THE DEEP CONNEXIONS OF THE CRANIAL NERVES. — 485 
and collaterals from the pyramidal tract of the opposite side enter the nucleus, and, ending 
around the cells, bring the nucleus into connexion with the motor area of the cerebral cortex. 
The pedicle of the superior olive ends partly within the nucleus of the abducent nerve (p. 482). 
Trigeminal or Fifth Nerve (nervus trigeminus).—The trigeminal nerve strikes 
its roots deeply into the brain and establishes a connexion with it which extends 
from the upper part of the mesencephalon above to the level of the second cervical 
nerve below. No other cranial nerve presents so extensive a connexion (Fig. 
356, p. 479). It is composed of two roots—a large afferent or sensory root and 
a small efferent or motor root. Both roots appear close together on the surface 
of the pons, rathet nearer its upper border than its lower border, and in the same 
line as the facial and auditory nerves. 
The sensory root of the fifth nerve is composed of fibres which arise outside the 
brain from the cells of the Gasserian ganglion. They end within the brain in two 
Superior medullary velum 
or valve of Vieussens 
Superior cerebellar peduncle— 
: Floor of 
oad _~ ventricle IV. 
Posterior 
longitudinal 
Mesencephalic root of the fifth nerve—__ 
fasciculus 
Motor nucleus of the fifth nerve 
Motor root of the fifth y pom naue 
Motor root of the fifth nerve ifr eae a 
Tae reticularis 
Sensory nucleus of the fifth nerve— 
Superior olive— : | Corpus 
= trapezoides 
Sensory root of 
fifth nerve —~/ 
Transverse 
==, fibres of pons 
Middle peduncle 
of cerebellum 
Fic. 360.—SECTION THROUGH THE PONS VAROLII OF THE ORANG, AT THE LEVEL OF THE NUCLEI 
OF THE TRIGEMINAL NERVE. . 
nuclei of termination. One of these is situated in the pons and is termed the 
sensory nucleus of the trigeminal nerve, and the other is a long column of 
gelatinous gray matter, which is directly continuous below with the substantia 
gelatinosa Rolandi of the spinal cord. 
The sensory nucleus (Fig. 360) is an oval mass of gray matter which is placed 
halfway up the pons in the outer part of its tegmental portion. It lies close to 
the outer surface of the pons and immediately subjacent to the ventral submerged 
margin of the superior cerebellar peduncle. It is directly continuous with the 
substantia gelatinosa Rolandi, and may be regarded as being merely the enlarged 
upper end of that column of gray matter. 
The sensory root of the fifth nerve, on reaching the sensory nucleus, divides into 
two parts (Fig. 356, p. 479). A portion of the fibres enter that nucleus and end 
within it, but the great proportion of the fibres turn sharply downwards and form 
the spinal root (tractus spinalis: the ascending root of most text-books). This root 
