246 THE ANATOMY OF THE HORSE. 



from the opposite side of the cord at the decussation. These decus- 

 sating fibres are furnished mainly by the lateral column, but partly 

 also from the superior column. The fibres of the inferior pyramid are 

 continued to the pons through the cerebrum. 



The olivary fasciculus of fibres is derived from the inferior column 

 of the cord on the same side, and it is continued through the pons to 

 the cerebrum. 



The restiform body derives its fibres from all three columns of the 

 cord on the same side, but in greatest proportions from the superior 

 column. It enters |the cerebellum, of which it forms the posterior 

 peduncle. The superior pyramid derives its fibres from the innermost 

 part of the superior column of the cord on the same side, and its fibres 

 are continued through the pons to the cerebrum. 



The medulla oblongata shows the superficial origin of the last seven 

 cranial nerves. 



THE PONS VAROLII (PLATE 33). 



The pons Varolii rests on the basilar process, in front of the medulla 

 oblongata. In front of it the crura cerebri appear. Its inferior face 

 is convex in both directions, and has a faint median furrow. The 

 superior face forms the anterior part of the floor of the 4th ventricle. 

 Its extremities are curved upwards to enter the cerebellum, of which 

 they form the middle peduncles. The pons consists of white and grey 

 nerve matter. The nerve fibres of the white matter are arranged in two 

 sets — a transverse and a longitudinal. The transverse fibres consist of 

 the surface fibres of the pons, and of deeper fibres separated from these 

 by the longitudinal set. It is these transverse fibres that curve upwards 

 at either extremity of the pons to enter the cerebellum as its middle 

 peduncle, and they accordingly play the part of a commissure to the 

 right and left halves of the cerebellum. The longitudinal fibres are the 

 forward continuation of the longitudinal fibres of the medulla oblongata, 

 minus the restiform bodies. In front of the pons these longitudinal fibres 

 are continued as the crura cerebri. The grey matter of the pons occurs 

 within its substance, and at the floor of the 4th ventricle. To a group 

 of pigmented nerve cells in the latter position the term locus coeruleus 

 is applied. 



The pons shows the superficial origin of the 5th cranial nerve, by two 

 distinct roots springing from its lateral aspect. 



THE CEREBELLUM (PLATES 34 AND 35). 



The cerebellum is superposed to the medulla and pons, and 

 lies under the supra-occipital division of the occipital bone. The 

 tentorium cerebelli arches downwards in front of it, and isolates 



