684: 



THE CENTRAL AXIS OF TEE NEBVOVS SYSTEM. 



the corpus resiiforme ; an inferior, represented by the corpus pyramidale ; 

 and the third, or intermediate of the other two. These three fasciculi are 

 only the continuation of those we have recognised in the cord itself, and 

 whose properties they share — the first being sensitive, and the others motor. 



The superior fasciculus, or 

 ^^' ' corpus restiforme, lying, at its 



posterior extremity, beside its 

 fellow of the opposite side, is 

 separated from it for the greater 

 part of its extent by the excava- 

 tion that constitutes the floor of 

 the fourth ventricle. It rests on 

 the external part of the lateral 

 fasciculus. At the extremity of 

 the pons Varolii is given off a 

 small branch that forms the pos- 

 terior cerebellar peduncle ; it 

 then continues its course on the 

 side of the posterior ventricle, 

 soon joins the anterior cerebellar 

 peduncle, which is above it, and 

 DISSECTION OF THE MEDULLA OBLONGATA, SHOWING with it passes Dencath the cor- 

 THE CONNECTION OF ITS SEVERAL FASCICULI, OR pora quadrigemiua. 



The inferior fasciculus, the 

 thinnest of the three, comprises, 

 as has been said, all that portion 

 of the bulb which constitutes 

 the pyramid. But when this 

 eminence is null, or but slightly 



STRANDS. 



A, Corpus striatum ; E, Thalamus opticus ; C, D, Cor- 

 pora quadrigemina ; E, Commissure connecting 

 them with the cerebellum ; F, Corpora restifor- 

 mia ; P, P, Pons Varolii ; sf, s^, Sensory tract ; 

 mi, mi, Motor tract ; g, Olivary tract ; p^ Pyrami- 

 dal tract ; og^ Olivary ganglion ; op, Optic nerve ; 



^71^°^,^ *?'."''^ P"'"' (motor); 55, Sensory root ^^rked, we ought to recoinise 

 01 tii6 nitn. pail . ii'i>*ii*i t • i e 



the limits which separate it from 

 the lateral fasciculus by the line of insertion of the roots of the great 

 hypoglossal nerve, supposed to be prolonged to the pons Varolii, near the 

 point of emergence of the external motores oculorum nerve. Its fibres 

 partly intercross with those of the opposite fasciculus, in the bottom of 

 the middle fissure. They all pass above or across the transverse fasciculi 

 of the pons, to constitute the inferior plane of fibres of the cerebral 

 peduncles. 



The lateral or intermediate fasciculus of the bulb, comprised between the 

 line of insertion of the hypoglossal nerve-roots, and those of the motor roots 

 proper to the glosso-pharyngeal, pneumogastric, and spinal nerves, differs 

 but little from the inferior cord. By a portion of its upper face it forms 

 the floor of the fourth ventricle. After leaving the pons Varolii, like the 

 pyramidal fasciculus, it goes to assist in the formation of the cerebral 

 peduncles, and particularly of their triangular oblique fasciculus. 



In examining, collectively, at these peduncles, the medullary fasciculi 

 prolonged into the isthmus, we observe nearly the same order of superposition 

 as in the bulb ; but it is no longer possible to distinguish them clearly from 

 each other, they being confounded with those of the opposite side. Their 

 fibres can be seen prolonged in a mass beneath the corpora quadrigemina, 

 across the proper substance of the thalami optici, and passing into the 

 corpora striata, to disappear on each side, like a fine expanding sheath, in the 

 middle of the cerebral hemispheres. 



