610 



THE BRAIN. 



for connecting this root with the collection of gray matter called " locus csd- 

 ruleus." (Fig. 136, I. c.). 



We may probably regard this descending root as belonging to the motor 

 division of the nerve ; but it is stated that many of the fibres of this root 

 pass into the sensory root, eventually finding their way, according to some 

 observers, into the ophthalmic branch. 



The sensory root may be similarly traced into a nucleus, the sensory 

 nucleus (Figs. 138 and 135, V. s.) lying lateral to the motor nucleus, and 

 connected with this is the striking tract of fibres, to which already we have 

 so frequently alluded, and which is called the ascending root of the fifth 



nerve. 



This ascending root begins as a bundle or bundles of few fibres which 

 may be traced backward as far, at least, as the level of the second cervical 

 nerve, and is soon conspicuous in transverse sections (Figs. 132 et seq., V. a.) 

 as a semilunar patch of white matter forming a sort of cap on the outside of 

 the swollen caput of the posterior horn, between this structure and the 

 longitudinal fibres which are beginning to form the restiform body on the 



Through the Crus and Anterior Corpora Quadrigemina. (Sherrington). One-half only is shown 

 in the line 114, Fig. 131. Py. the pyramidal portion of the pes ; jFV.the region of the pes occupied 

 by fibres from the frontal portion of the cortex; Pr. 0. 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, 1. 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. 1. lateral, and C. g. m. median 

 corpus geniculatum ; P?;r. pulvinar of optic thalamus ; A. Q. n. nucleus or gray matter of anterior 

 corpus quadrigeminum ; III. n. nucleus of III. third nerve ; III/ rootlets 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; Aq. aqueduct surrounded by cerebral gray matter. 



surface. Passing upward, 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. 133, 134). Passing still forward, be- 

 yond 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 

 rounds and joins the sensory root. 



