768 



THli CENTRAL AXIS OF THE NERVOUS SYSTEM. 



On the middle line there is a well-marked fissure — a continuation of the 

 inferior fissure of the cord — which lies between two very elongated prominences 

 that are sometimes but httle apparent, and which, from their form, are named 

 the corpora pyramidalia (Fig. 424, p, p). The base of these pyramids touches 



Fig. 424. 



GENERAL VIEW OF THE HORSE'S BRAIN (INFERIOR FACE). 



B, Medulla oblongata; P, p, pyramids of ditto. 1, Internal root of the spinal accessory nerve; 2, 

 external roots of ditto ; 2', roots of the pneumogastric nerve ; 3, root of the auditory nerve ; 4, root 

 of the facial nerve ; 5, sixth nerve ; 6, root of the fifth nerve; 6', H", motor and sensory roots of 

 the fifth nerve. P.c, P.c, crura cerebri. 7, Third nerve ; 8, optic commissure ; 10, fissure of 

 Sylvius; 11, pituitary gland ; 12. extra-ventricular nucleus of the corpus striatum ; 13, external 

 root of the olfactory bulb; 14, internal root of ditto; 15, olfactory bulb; 16, 16, grey nuclei 

 from which proceed the olfactory nerves ; 17, lateral lobe of the cerebellum; 18, temporal lobe 

 of the brain; 19, first temporal convolution; 20, lobule of the curved plait; 21, gyrus rectus; 

 22, frontal lobe (antero-external face). 



the pons Varolii, and their apex is insensibly lost, posteriorly, on reaching the 

 spinal cord. 



Outwardly is an almost plane surface, bordered anteriorly by a transverse 

 band (Fig. 330) which lies immediately behind the pons Varolii ; sometimes it is 

 covered for the greater part of its extent by a very thin expansion of arciform 



