THE PONS (VAROLII). 269 



into lateral halves by the sulcus basilaris, containing the basilar 

 artery; and is bounded laterally by a sagittal plane cutting the 

 root of the trigeminal nerve. Vertically the surface is slightly 

 convex, and is markedly so from side to side. It shows trans- 

 verse striations, which converge laterally, due to the fibers that 

 form it and enter the brachia pontis of the cerebellum. The 

 fibers of the anterior surface are not exactly transverse in direction. 

 Those at the superior end of the pons bend downward (fasciculus 

 obliquus) and form a rounded margin, which covers the lower 

 part of the bases pedunculi of the mid-brain; at the inferior ex- 

 tremity of the pons, the fibers are convex downward and partially 

 conceal the pyramids of the medulla oblongata. The two roots 

 of the fifth nerve (trigeminal) are attached to the lateral border 

 (Henle) of this surface, a little above the middle. 



The posterior surface of the pons is concealed by the cere- 

 bellum (Fig. 88). It is free in its middle part, where it forms the 

 floor of the superior half of the fourth ventricle (Fig. 86). The 

 ventricular area of the posterior surface is completely concealed 

 by the superior medullary velum. If examined, it is found to be 

 divided into lateral halves by a median longitudinal groove. 

 Each half presents in its posterior part a rounded eminence, 

 the colliculus facialis, which flanks the median furrow and is in 

 turn bounded, laterally, by a linear valley, the sulcus limitans, 

 lying near the brachium conjunctivum cerebelli and parallel with 

 it. The inferior end of the valley is called the fovea superior; 

 its upper part has a bluish tint, due to underlying pigmented 

 cells, and is called the locus caruleus. Attached Area. Lateral 

 to this ventricular area, the posterior surface of the pons is attached 

 to the restiform body and the conjoined arms of the cerebellum. 

 The restiform bodies enter the surface near the lower end of the 

 pons and then bend downward into the medulla oblongata; while 

 the brachia conjunctiva, in their course up to the cerebrum, 

 partly imbed themselves hi the lateral part of the posterior surface 

 and form the walls of the fourth ventricle. The lateral fillet 

 issues from this surface just external to the brachium conjunc- 

 tivum. It runs obliquely across the upper end of the brachium 

 to the inferior colliculus of the corpora quadrigemina, and pro- 



