THE HIND-BRAIN OR RHOMBENCEPHALON 785 



in the upper part of the medulla oblongata, lies between the lemniscus and the gray 

 substance of the rhomboid fossa. The longitudinal fibers in the reticularis grisea 

 are derived from the lateral funiculus of the medulla spinalis after the lateral 

 cerebrospinal fasciculus has passed over to the opposite side, and the dorsal spino- 

 cerebellar fasciculus has entered the inferior peduncle. They form indeterminate 

 fibers, with the exception of a bundle named the fasciculus solitarius, which is made up 

 of descending fibers of the vagus and glossopharyngeal nerves. The transverse 

 fibers of the formatio reticularis are the arcuate fibers already described (page 782). 



The Pons (pons Varoli). The pons or forepart of the hind-brain is situ- 

 ated in front of the cerebellum. From its superior surface the cerebral peduncles 

 emerge, one on either side of the middle line. Curving around each peduncle, close 

 to the upper surface of the pons, a thin white band, the taenia pontis, is frequently 

 seen; it enters the cerebellum between the middle and superior peduncles. Behind 

 and below, the pons is continuous with the medulla oblongata, but is separated 

 from it in front by a furrow in which the abducent, facial, and acoustic nerves 

 appear. 



Its ventral or anterior surface (pars basilaris pontis) is very prominent, markedly 

 convex from side to side, less so from above downward. It consists of transverse 

 fibers arched like a bridge across the middle line, and gathered on either side into 

 a compact mass which forms the middle peduncle. It rests upon the clivus of the 

 sphenoidal bone, and is limited above and below by well-defined borders. In the 

 middle line is the sulcus basilaris for the lodgement of the basilar artery; this sulcus 

 is bounded on either side by an eminence caused by the descent of the cerebrospinal 

 fibers through the substance of the pons. Outside these eminences, near the upper 

 border of the pons, the trigeminal nerves make their exit, each consisting of a 

 smaller, medial, motor root, and a larger, lateral, sensory root; vertical lines 

 drawn immediately beyond the trigeminal nerves, may be taken as the boundaries 

 between the ventral surface of the pons and the middle cerebellar peduncle. 



Its dorsal or posterior surface (pars dorsalis pontis} , triangular in shape, is hidden 

 by the cerebellum, and is bounded laterally by the superior peduncle; it forms 

 the upper part of the rhomboid fossa, with which it will be described. 



Structure (Fig. 701). Transverse sections of the pons show it to be composed 

 of two parts which differ in appearance and structure: thus, the basilar or ventral 

 portion consists for the most part of fibers arranged in transverse and longitudinal 

 bundles, together with a small amount of gray substance; while the dorsal tegmental 

 portion is a continuation of the reticular formation of the medulla oblongata, 

 and most of its constituents are continued into the tegmenta of the cerebral 

 peduncles. 



The basilar part of the pons consists of (a) superficial and deep transverse 

 fibers, (b) longitudinal fasciculi, and (c) some small nuclei of gray substance, 

 termed the nuclei pontis which give rise to the transverse fibers. 



The superficial transverse fibers (fibrce pontis superficiales) constitute a rather 

 thick layer on the ventral surface of the pons, and are collected into a large 

 rounded bundle on either side of the middle line. This bundle, with the addition 

 of some transverse fibers from the deeper part of the pons, forms the greater part 

 of the brachium pontis. 



The deep transverse fibers (fibres pontis profundce) partly intersect and partly 

 lie on the dorsal aspect of the cerebrospinal fibers. They course to the lateral 

 border of the pons, and form part of the "middle peduncle; the further connections 

 of this brachium will be discussed with the anatomy of the cerebellum. 



The longitudinal fasciculi (fasciculi longitudinales) are derived from the cerebral 

 peduncles, and enter the upper surface of the pons. They stream downward on 

 either side of the middle line in larger or smaller bundles, separated from each 

 other by the deep transverse fibers; these longitudinal bundles cause a forward 

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