GREY SUBSTANCE OF THE PONS 



831 



ascends the medulla, dispersed in the reticular formation, and therefore in a more ventral posi- 

 tion than that of the direct cerebellar tract. In this position it becomes enclosed by the 

 fibres of the pons, and so it passes upward, beyond the pons, around the lateral lemniscus to 

 the brachium conjunctivum, and there turns back to enter the cerebellum by way of its supe- 

 rior peduncle. Certain clinical phenomena, probably purely psychological, have been alleged to 

 indicate that some of the fibres of Gowers' tract pass on to the cerebrum instead of turning in 

 the medullary velum to enter the cerebellum. 



The dorsal part of a transverse section through the upper part of the pons contains the 

 superior cerebellar peduncles [brachia conjunctival instead of the restiform bodies or inferior 

 peduncles. Instead of the cerebellum forming the roof of the fourth ventricle, in this region 

 the roof is formed by the anterior medullary velum bridging the space between the two brachia 

 conjunctiva. Adhering upon the meduUary velum is the lingula cerebelli — the superior and 

 ventral extremity of the superior vermis. This is the only portion of the cerebellum attached 

 to this region. 



The lemniscus (fillet) is found more lateral than at the inferior border of the pons, and is 

 divided into the medial lemniscus and lateral lemniscus proper. The lateral lemniscus has shifted 

 dorsally until in this region it courses in the dorso-lateral margin of the section external to the 

 brachium conjunctivum. The mesencephalic root of the masticator nerve occurs in the dorso- 



FiG. 657. — Diagram showing Connections of the Fibres of the Pons. 

 The plane of the section is obliquely transverse or parallel with the direction of the brachia pontis 



Lateral nucleus of vestibular 

 nerve 



— —Restiform body 



/ Medial descending 

 "cerebro-pontile path 



--Medial lemniscus 



erebro- fchiefly frontal) 

 pontile path 



Longitudinal (pyramidal) fasciculi 



lateral margin of transverse sections through this region, and this and the trigeminus are the 

 only cranial nerves repi'esented here. 



The transverse fibres of the ventral part of the section (pons proper), and therefore the 

 brachia pontis, consist of fibres coursing in opposite directions. Many are fibres which are out- 

 growths of the Purkinje cells of the cortex of the cerebellar hemispheres, and pass either directly 

 to the cerebellar hemisphere of the opposite side or turn dorsalward in the raphe to course 

 longitudinally in the brain-stem both toward the spinal cord and toward the mesencephalon. 

 Others terminate in the grey substance (nuclei) of the pons. Others are fibres which arise in 

 the grey substance of the pons and pass to the cerebellar hemispheres, and stUl others are 

 the cerebro-pontile fibres, from the temporal, occipital and frontal lobes. 



The grey substance of the pons [nuclei pontis] occurs quite abundantly. At the inferior 

 border of the pons it is found concentrated about the then more accumulated bundles of the 

 emerging pyramids, and serial sections show it to be a direct upward continuation of the arcuate 

 nuclei of the medulla oblongata below. Higher up it is dispersed throughout the central area 

 in the interspaces between the transverse pontile and longitudinal pyramidal fascicuh. A 

 large portion of the nerve-fibres passing through it are thought to be interrupted by its cells, 

 which thus serve as links in some of the neurone chains represented by the fibres of the pong. 

 Of the more important of such relations, the following are said to exist: — 



(1) Fibres which arise in the cortex of one cerebellar hemisphere and terminate about cells 

 of the nucleus pontis of the same and opposite side of the mid-line. These cells give off axones 

 which pass to the other cerebellar hemisphere. In this relation the nuclei of the pons are 

 analogous to the arcuate nuclei, save that the cerebellar fibres interrupted m the former are 

 connected with the cerebellum by way of the brachia pontis uistead of the restiform bodies. 



