830 THE NERVOUS SYSTEM 



of the pons, and their position and course have been described above. The pons proper 

 (the bridge) consists of a mass of transversely running fibres continuous on either side into 

 the brachia pontis or middle cerebellar peduncles. In the animal series the relative amount 

 of these fibres varies with the size of the cerebellum upon which they are dependent. They 

 are relatively more abundant in man than in other animals. 



In transverse sections the pons fibres are seen to course ventrally about the main axis of 

 the brain-stem, making it possible to divide the section into a basilar or ventral part and a dorsal 

 part {tegmentum). The fibres in their transverse and ventral course around the medulla oblon- 

 gata involve the pyramids. At the inferior border of the pons the fibres little more than separate 

 the pyramids as such from the main axis of the brain-stem, but more superiorly the pons fibres 

 pass through the pyramids, splitting them into the pyramidal fasciculi. These pyramidal or 

 chief longitudinal fibres of the pons are the continuation of the basal portion of the cerebral 

 peduncles through the pons, to emerge as the pyramids proper at its inferior border. They 

 occupy an intermediate or central area among the pons fibres of either side, leaving the periphery 

 of the pons untnvaded. The superficial pons fibres form the solid bundle of its ventral and lateral 

 periphery and the deep pons fibres form similar bundles dorsally enclosing the area of pyramidal 

 fasciculi (fig. 655). 



In transverse sections through the inferior portion of the pons, the dorsal or tegmental part 

 consists of structures continuous with and analogous to the structures of the medulla oblongata 

 immediately below, exclusive of the pyramids. In addition, this region contains the superior 

 olivary nucleus and the corpus trapezoideum. The significance of these structures and their 

 relation to the nucleus of termination of the cochlear nerve is shown in figs. 650, 651 and 652. In 

 this region the lemniscus (fiUet) changes from the sagittal to the coronal plane, and its 



Fig. 656. — Diagram showing the Rhombencephalic Course of Gowers' Tract and the 



Direct Cerebellar Tract. 



Brachium conjunctivum 



Dorsal spino-cerebellar fasciculus 

 (direct cerebellar tract) 



Superficial antero-lateral spino-cerebellar 

 fasciculus (Gowers' tract) 



lateral edges are becoming drawn outward and carry the lateral lemniscus of the regions 

 superior to this. The medial longitudinal fasciculus, left alone by the change in the arrangement 

 of the leminscus, maintains its dorsal position tliroughout the pons and mto the mesencephalon 

 above. The thalamo -olivary tract appears loosely collected in the dorsal part of the pons, 

 dorso-medial to the nucleus of the superior ohve. 



The restiform body acquires in this inferior region a more dorso-lateral position than in the 

 medulla below. Its fibres are beginning to turn upward in their course to the cerebellum mesial 

 to the brachium pontis. Here the restiform body is nearing completion, and the fibres now 

 contained in it may be summarised as follows: — 



(1) The fibres of the dorsal spino-cerebellar fasciculus (direct cerebellar tract) of the same 

 side. 



(2) Fibres from the nuclei of the fasciculus gracilis and fasciculus cuneatus of the same and 

 opposite side (external arcuate fibres). 



i'.i) Fibres to and from the inferior olives of the same and (chiefly) the opposite side (cere- 

 bello-olivary fibres). 



(4) Sensory cerebellar fibres from the nuclei of termination of the vagus, glosso-pharyngeus, 

 vestibular and trigeminus, vestibular especially, and from the cells of the reticular formation. 



(5) Descending fibres to tlic motor nuclei of the vagus and glosso-pharyngeal, and fibres 

 descending into the anterior marginal fasciculus of the spinal cord, the latter, however, being 

 in large part interrupted by cells in the nuclei of the vestibular nerve. 



(6) A few fibres arising from the arcuate nuclei. These nuclei are continuous superiorly 

 with the nuclei of the pons and .some of their fibres are described as entering the cerebellum by 

 way of the restiform body instead of by way of the brachium of the pons as in the levels above. 



The ascending fibres of th(! restiform body are distributed to the cortex of the vermis, the 



nucleus of the roof (fastigii), the nucleus dentatus, nucleus emboliformis, and nucleus globosus. 



Very few if any of the fibres ascending the cord in Gowers' tract enter the cerebellum by way 



of the restiform body. This tract (the superficial antero-lateral spino-cerebellar fasciculus) 



