1360 A MANUAL OF ANATOMY 



pass over, or through, the inferior olivary nucleus of that side, on 

 the dorsal aspect of which they are collected into a distinct tract. 

 This tract, arching backwards, applies itself to the restiform body, 

 on its deep aspect, and is thereby conducted to the cerebellar 

 hemisphere. Its fibres terminate in the cortex of the vermis 

 and cerebellar hemisphere. The olivo-cerebellar arcuate fibres con- 

 stitute the olivo-cerebellar tract, which connects the inferior olivary 

 nucleus of one side with the cerebellar hemisphere of the opposite 

 side. 



Fillet. — ^The fillet, or lemniscus, as present in the bulb, is a well- 

 marked tract of fibres which lies on the dorsal aspect of the pyramid 

 close to the raphe. As just stated, its fibres are derived from the 

 lemniscal deep arcuate fibres of the opposite side. In the lower 

 part of the bulb the fillet and dorsal longitudinal bundle are closely 

 related. In the upper part of the bulb, however, as previously 

 stated, the dorsal longitudinal bundle is displaced dorsalwards by 

 the developing fiUet, and the fillet, now distinct from the dorsal 

 longitudinal bundle, lies on the ventral aspect of that bundle, and 

 on the dorsal aspect of the pyramid. The ventral region of the 

 bulb is thus traversed by three longitudinal tracts, all of which lie 

 close to the median line. These tracts are related to each other in 

 the following order from before backwards : 



Pyramid. 



Fillet. 



Dorsal longitudinal bundle. 



Olivo-cerebellar Tract. — ^This tract has already been described in 

 connection with the olivo-cerebellar deep arcuate fibres. 



Raphe of tlie Medulla Oblongata. — ^The raphe of the bulb occupies 

 the median plane above the decussation of the pyramids, and is 

 composed of fibres which, for the most part, cross obliquely from 

 one side to the other. These fibres represent (i) the anterior 

 superficial arcuate fibres, (2) the lemniscal deep arcuate fibres, and 

 (3) the olivo-cerebellar deep arcuate fibres. A few fibres pass 

 ventro-dorsally, and some are disposed longitudinally. The fibres 

 are therefore arranged in an intersecting manner. 



Central Canal of tlie Medulla Oblongata. — ^The central canal of the 

 spinal cord is prolonged upwards through the lower or closed part 

 of the bulb. As it ascends it is gradually displaced backwards, 

 first by the decussation of the pyramids, and afterwards by the 

 decussation of the fillets. It is surrounded by a thick layer of grey 

 matter, which is derived from the basal portions of the ventral and 

 dorsal grey cornua of the spinal cord. Superiorly, at the level of 

 the calamus scriptorius, it opens into the lower part of the fourth 

 ventricle in the angle between the two diverging clavse. The grey 

 matter which surrounds the canal is now spread out and forms a 

 thick covering over the lower part of the ventricular floor, as pre- 

 viously stated. 



Areas of Flechsig. — These areas involve the whole substance of the bulb, 

 and aie mapped out by the funiculi of the hypoglossal and pneumogastric 



