MINUTE STRUCTURE OF THE MEDULLA OBLOXGATA. 519 



(faisceaux innomine's), appearing on the back of the pons Varolii, in the 

 upper part of the floor of the fourth ventricle. 



3. The anterior columns having reached the apex of the anterior pyramids, 

 are thrust aside from their median position by the decussating fibres derived 

 from the lateral columns, and are then distributed in three divisions. (1,) A 

 very small division, ascends obliquely backwards beneath the olive, and joins 

 the restiform body (Solly). (2,) Another division passes directly upwards, 

 its fibres embracing the olivary nucleus, above which they are again collected 

 together, and are joined by other fibres arising from the nucleus, so as to 

 form the olivary fasciculus ; this ascends through the pons and at the side 

 of the cerebral peduncle under the name of the fillet, and reaches the corpora 

 quadrigemina and the cerebral hemispheres. (3,) The remaining division of 

 the anterior column ascends into the anterior pyramid, forming its outer 

 part. The anterior pyramids therefore are composed of fibres from the 

 lateral and anterior columns, and are continued up through the pons into 

 the peduncles of the cerebrum. 



It is to be remembered, however, that the separation between these 

 different tracts of white fibres cannot be clearly followed out through the 

 whole structure of the medulla oblongata, but that they are more or less 

 blended with one another. 



Grey matter of the medulla oblongata followed upwards from the cord. The 

 central canal of the spinal cord, together with the grey matter which surrounds it, 

 approaches nearer and nearer to the back of the medulla oblongata as it ascends, until 

 it terminates in the calamus scriptorius. 



The anterior pyramids are free from grey matter in their interior, and are separated 

 from the rest of the medulla by strong septa of connective tissue, and from one 

 another by a raplie, which extends back to the grey matter surrounding the central 

 canal, and which contains mesial horizontal fibres, named septal. The posterior 

 cornua of grey matter in the lower part of the medulla oblongata extend transversely 

 outwards from the central canal, and higher up stretch outwards and forwards to the 

 surface. The substantia gelatinosa is swollen out into a mass which appears circular 

 in a transverse section, and is named the grey tubercle of Rolando. The anterior 

 cornua, together with the intermedio-lateral tract, which had re-appeared at the upper 

 end of the cord, vanish in the form of elongated radiating streaks ; and between them 

 and the anterior pyramids appear the olivary nuclei, unconnected with the system of 

 grey matter prolonged from the spinal cord. Behind the posterior cornua two new 

 cornua make their appearance one extending into the processus cuneatus and the 

 other into the posterior pyramid, and both of them increasing in size as the posterior 

 pyramids increase. In the neighbourhood from which these and the posterior cornua 

 spring there is seen in transverse sections a limited bundle of white fibres, the round 

 fascicle of Stilling. In the upper part of the medulla oblongata the grey matter is 

 principally spread out on the floor of the fourth ventricle. (Reichert, op. cit., part 

 2nd, plates I. and II.) 



According to the observations of Stilling, part of the grey matter at the back 

 of the medulla forms special deposits or nuclei, which are connected with the roots 

 of the spinal accessory vagus, glosso-pharyngeal, and hypoglossal nerves. Of these 

 nuclei, the first or lowest is concealed in the substance of the medulla; whilst 

 those which are situated higher up gradually appear in the floor of the fourth 

 ventricle as small angular eminences pointing downwards, near the apex of the calamus 

 scriptorius. The first nucleus proceeding from below is that for the spinal accessory 

 nerve. It reaches some way down in the cord, and is there lost in the intermedio- 

 lateral tract. Above this nucleus, and close to the middle of the medulla, is another, 

 the second, commencing higher up, and connected with the hypoglossal nerve, the 

 roots of which, coming forward between the anterior pyramid and the olivary body, 

 appear at the surface in the depression between those parts. Continuing to ascend, 

 these two nuclei reach the back of the medulla, and then make their appearance in 

 the floor of the fourth ventricle. Higher up, the nucleus for the spinal accessory 



