AREAS OF THE MEDULLA OBLONG AT A 867 



(c) The funiculus lateralis is a longitudinal prominence which gradually en- 

 larges cephalad into a slight tubercle, the tuberculum cinereum (tuberculum Rolandi), 

 marking the approach of the gelatinosa to the surface so as to form a prominence 

 at a level with the lower border of the olive. 



The restiform body (restis; corpus restiforme) occupies the upper dorsolatera) 

 area of the medulla oblongata on each side, lying between the floor of the fourth 

 ventricle and the roots of the vagus and glossopharyngeal nerves. This structure 

 might at first glance appear to be the continuation of the three funiculi just 

 described. But as a matter of fact it is made up of the direct spinocerebellar tract, 

 a set of external or ectal arcuate fibres (fibrae arcuatae externae) and a set of internal 

 or ental arcuate fibres (fibrae arcuatae internae). Each restiform body assists in 

 forming the lower part of the lateral boundaries of the fourth ventricle and then 

 enters the cerebellum as the inferior peduncle of that body. 



The Pons (pans Varolii). The pons is a prominent white mass on the ventral 

 aspect of the brain stem which is interposed between the medulla oblongata 

 and the crura cerebri. It is convex from side to side and its fibres, running chiefly 

 in a transverse arched direction, are gathered into rounded, compact strands 

 on either side, to continue as the middle peduncles into the white substance of 

 the corresponding cerebellar hemisphere. The fibre bundles of the pyramidal 

 tracts thread their way through the pons on either side of the median plane and 

 small aggregations of gray substance (nuclei pontis} are packed in the intervals 

 between the transverse pontile and longitudinal pyramidal fibre bundles. 



The Basilar Surface (pars basilaris pontis). The basilar or ventral surface of the 

 pons is in relation with the basilar process of the occipital and the dorsum sellae 

 of the sphenoid. A shallow mesal groove lies between the eminences produced 

 by. the pyramidal tracts in their course through the pons. The groove is called 

 the basilar groove (sulcus basilaris), as the basilar artery is usually, accommo- 

 dated in it; the artery is not, however, a factor in the production of the groove. 

 The large sensor and small motor root bundles of the trigeminal nerve pierce the 

 mass of the pons near the anterior pontile border, and a line drawn from this 

 nerve root to that of the facial nerve is usually employed as an arbitrary boundary 

 between the pons proper and the middle peduncle of the cerebellum. The 

 abducent nerve emerges from the posterior pontile border (prepyramidal part); 

 the facial and acoustic nerves are attached farther laterad. 



While most of the superficial fibre bundles of the pons are seen to arch trans- 

 versely, certain small compact bundles 1 are seen to extend in an obliquely longitu- 

 dinal direction from the region of the trigeminal nerve root to and among the 

 roots of the facial and acoustic nerves. 



The Pars Dorsalis Pontis (preoblongata; parsmetencephalica medullaeoblongatae). 

 The pars dorsalis pontis, or tegmental part, is not sharply demarcated from the 

 medulla oblongata or the tegmentum and crusta of the mid-brain, and the margins 

 of the pons on the ventral surface afford only arbitrary boundary lines; for in the 

 vertebrate series the pons varies greatly in width and its margins can hardly be 

 accepted as the boundaries of a definite brain segment. The dorsal surface 

 of the pars dorsalis pontis is continuous with that of the oblongatal ventricular 

 surface, and its description more properly belongs to a consideration of the anatomy 

 of the fossa rhomboidalis or "floor of the fourth ventricle." 



Fourth Ventricle of the Brain (ventriculus quartus). In a previous section 

 on brain development it has been pointed out how the growth changes and differ- 

 entiations in the hind-brain differ from those of the rest of the neural tube in that 

 there is a marked disproportion in the degree of growth in the dorsal and ventral 

 walls. While the ventral wall thickens greatly throughout to form the pons oblon- 



corp 



1 Called the inter-rndicular pons tract by E. C. Spitzka C1884), and more recently described as part of the 

 rpu8 pontobulbare by Essick (American Journal of Anatomy, vii, 1 ). 



