738 



Special grey 

 masses. 



DISSECTION OF THE BRAIN. 



and the bases of the anterior horns are exposed, constituting the grey layer in 

 the floor of that cavit r . 



Special deposits of grey matter. These are the olivary nucleus, which 

 has just been examined, some groups of nerve-cells at the back of the medulla 

 oblongata forming nuclei of origin for several cranial nerves, which will be 

 noticed in connection with the anatomy of the fourth ventricle, and a few 

 small masses of grey substance of the front of the medulla beneath the 

 superficial arciform fibres. 



PONS VAROLII. 



POMS: The PONS VAROLii is situate above the the medulla oblongata, and 



position, between the hemispheres of the cerebellum. In its natural position 



in the skull it lies below the opening in the tentorium cerebelli, 



sup. meet, velum 



dorsal grey laye 



rettcula 

 formation, 



sup. peduncle 

 of cerebellum 



inf. peduncle 

 inid. peduncle 



deep tranc uerse 

 fibres 



pyramidal jn,bres- 



superficial transverse fibres. 



Fia. 266. DIAGRAM OF A TRANSVERSE SECTION THROUGH THE LOWER PART 



OF THE PONS, SHOWING ITS CHIEF CONSTITUENTS. 



form, 

 surfaces 



borders, 

 and sides. 



It consists 

 of ventral 



and dorsal 

 portions. 



Dissection 

 to expose 

 the fibres. 



resting against the hinder part of the body of the sphenoid bone. It 

 is nearly of a square shape, though it is rather wider from side to 

 side, in which direction it measures about an inch and a half. 



The anterior surface is convex and prominent on each side, but 

 marked along the middle line by a groove in which the basilar artery 

 lies. By the opposite surface the pons forms the part of the floor of 

 the fourth ventricle. 



The upper border is the longer, and arches over the crura cerebri. 

 The lower border is nearly straight, and projects above the medulla 

 oblongata. On each side the pons is continued into the middle 

 peduncle of the cerebellum, and the fifth nerve issues through it on 

 each side. 



STRUCTURE. The ventral or anterior half of the pons consists of 

 transverse fibres which are in part of their extent divided into two 

 layers by the prolongation upwards through them of the fibres of the 

 pyramids of the medulla oblongata. The dorsal or posterior half is 

 a continuation of the reticular formation, with the grey layer of the 

 floor of the fourth ventricle, from the medulla oblongata. 



Dissection. The superficial transverse _ fibres of the pons have 



