964 



NUCLEI OF CRANIAL NERVES. [BOOK m. 



horn, between this structure and the longitudinal fibres which are 

 beginning to form the restiform body on the surface. Passing 

 upwards, and continually augmenting in bulk, the root clings, as 

 it were, to the gelatinous substance of the caput of the posterior 

 horn, and sinks with it inwardly and ventrally as this becomes 

 covered up first by the restiform body and subsequently by the 

 issuing trunk of the great eighth or auditory nerve (Figs. 110, 

 111). Passing still forward, beyond the disappearing gelatinous 

 substance, the root, still growing larger and divided into several 

 distinct bundles, runs into the reticular formation of the pons 

 and, reaching the level of the sensory nucleus, suddenly bends 

 round and joins the sensory root. 



This ascending root differs from the descending root in not 



FIG. 114. THROUGH THE CRUS AND ANTERIOR CORPORA QUADRIGEMINA. 

 (One half only is shewn.) (Sherrington.) 



(In the line 114, Fig. 108.) 



Py. the pyramidal portion of the pes. Fr. the region of the pes occupied by fibres 

 from the frontal portion of the cortex. Pr. O. the region occupied by fibres 

 coming from the occipital portion of the cortex, y. fibres coming from the 

 fillet. Op. the optic tract. F. the fillet, I. the lateral portion, m. the median 

 portion. I. the posterior longitudinal bundle. B. a. the brachium of the 

 anterior corpus quadrigeminum. x. fibres from the posterior commissure of 

 the cerebrum, r. raphe. S. n. substantia nigra. R. n. red nucleus. C. g. I. 

 lateral, and C. g. m. median corpus geniculatum. Pvr. pulvinar of optic 

 thalamus. A. Q. n. nucleus or grey matter of anterior corpus quadrigeminum. 

 III. n. nucleus of III. third nerve. III'. Eootlets from the dorsal part of 

 III. n. the nucleus of the third nerve which cross the median line to emerge 

 with rootlets derived from the nucleus of the opposite side. s. m. superficial 

 layer of fibres of the ant. corp. quad. d. m. deep layer. V. d. descending root 

 of the fifth nerve. Aq. aqueduct surrounded by cerebral grey matter. 



having conspicuously attached to it any collection of nerve cells ; 

 in this respect it resembles the ascending root of the glosso- 

 pharyngeal, and we may add part of the posterior root of an 



