608 



THE BRAIN. 



nucleus (Fig. 138, VI.), lying at the level of the hinder part of the pons, 

 and therefore of the front part of the fourth ventricle, in the central gray 

 matter of the floor of the ventricle, or rather just between it and the reticular 

 formation, a little on one side of the median line (Fig. 134, VI.). A slight 

 swelling of the floor of the fourth ventricle, eminentia teres, marks its posi- 

 tion (Fig. 138, e. t.). The nucleus contains fairly large nerve-cells, with dis- 

 tinct axis-cylinder processes. These are gathered at the median side of the 

 nucleus to form the thin root, which, passing ventrally and laterally, at some 

 little distance from the median raphe, through the reticular formation, runs 

 backward above the pyramidal bundles of the pons, and finally comes to 

 the surface at the hinder edge of the pons, opposite the front end of the 

 pyramid (Fig. 131, C.). 



ar.P 



Through the Pons at the Exit of the Fifth Nerve. (Sherrington.) In the line 112, Fig. 131. 

 C. R. remains of restiform body ; S. P. superior peduncle of the cerebellum ; F. m. median ; F. I. 

 lateral fillet ; T. R., tegmental reticular formation ; tr. P. superficial transverse fibres of the pons ; 

 I. posterior longitudinal bundles ; V. s. superior vermis (sections of three folia are shown, one 

 being detached ; between them the intervening sulci laid open by the section are seen) : IVu. 

 valve of Vieussens or anterior velum : r. raphe; Py. pyramidal fibres ; gr. P. gray matter of the 

 pons ; s. o., siiperior olive ; t., placed on the left side indicates the position of a bundle of longi- 

 tudinal fibres which may be traced forward into the subthalamic regions ; V. m. motor nucleus; 

 V. s., sensory nucleus; and V. roots of the fifth nerve. 4th, fourth ventricle; shading of cen- 

 tral gray matter omitted as in Fig. 134. 



534. The fifth or trigeminal nerve. This nerve, as it comes to the sur- 

 face on the ventral aspect of the pons (Fig. 131, (7.), near the front edge, 

 at some distance from the median line, consists of two parts, a smaller motor 



