682 



NERVOUS SYSTEM. (NERVOUS CENTRES. THE ENCEPHALON.) 



yet to be discovered. The anatomical con- 

 nection of each anterior pyramid with the 

 spinal cord, however, affords some clue to it. 

 This takes place, it will be remembered, not 

 by the decussating fibres only, but by straight 

 and perpendicular ones also ; so that each py- 

 ramid is connected with both halves of the 

 spinal cord, first and principally with the op- 

 posite half; and, secondly, and by much fewer 

 fibres, with that of the same side. When those 

 parts of the brain are affected, with which the 

 decussating fibres are connected, the paralysis 

 will be crossed ; when, on the other hand, the 

 direct fibres are engaged, the paralytic affection 

 will occur on the same side of the body as that 

 on which the lesion has occurred. But even 

 on this explanation it is difficult to understand 

 how these latter cases should be of such rare 

 occurrence, and still more, how hemiplegia is 

 so frequently accompanied with a perfect state 

 of sensation and motion on the other side. In 

 the present state of our knowledge, however, 

 this is the only contribution which anatomy 

 can offer towards the determination of this 

 difficult question. 



Of the rest; form bodies. The lateral, and, in 

 great part, the posterior portion of the medulla 



Fig. 386. 



D, 



D', 



+ 



Y, 



X, 



B, 



oblongata is formed on each side by a thick 

 and rounded rope-like column, called the corpus 

 restiforme. It is composed chiefly of fibrous 

 matter, and its constituent fibres take a lon- 

 gitudinal direction. There is no line of demar- 

 cation between them and the fibres of the spinal 

 cord, with the antero-lateral and posterior co- 

 lumns of which they seem to be continuous. 

 Traced upwards, the restiform bodies pass a 

 little outwards, and by their divergence con- 

 tribute to the increased size of the medulla 

 oblongata at its base. 



To see the connexions of these bodies com- 

 pletely, the posterior surface of the medulla 

 oblongata should be examined. The restiform 

 bodies form the greater part of this surface. 

 They increase in thickness as they ascend. 

 Their outer margin forms a gentle curve, which 

 is concave. Their inner border is connected in 

 its lower portion to two small bands of fibrous 

 matter, between which the posterior median 

 fissure is situate; these are the posterior py- 

 ramids (Y,fig. 386). In its upper portion, the 

 inner border of each restiform body is free, and 

 forms the outer boundary of a lozenge-shaped 

 depression, the fourth ventricle. Whilst the 

 connection of the cerebellum with the pos- 

 terior surface of the medulla oblongata is un- 

 disturbed, the exact relation of these bodies to 

 the ventricle cannot be seen. It is necessary 

 to raise up the inferior portion of the median 

 lobe of the cerebellum, to expose the cavity 

 of the ventricle; or this may be effected by 

 dividing the median lobe along the middle 

 line. 



Each restiform body ascends to the hemi- 

 sphere of the cerebellum of the correspond- 

 ing side. The whole of its fibres appear 

 to penetrate that organ, and contribute to 

 the formation of its crus, the middle layer 

 or peduncle of which it forms. This is very 

 well shown in the analytical figure at p. 

 667, (jig. 380,) where r is the restiform 

 \ body passing upwards and outwards into 

 iii\ the hemisphere of the cerebellum. 



\ The distinction between the restiform and 

 fi&jl olivary bodies on the surface is indicated 

 jijvjf by the line of origin of the eighth pair of 

 nerves, which may be said to emerge along 

 the anterior margin of the former. A nar- 

 row band of fibres, very distinct in some 

 brains, occupies the depression between the 

 posterior edge of the prominent olivary body 

 and the line of emergence of these nerves. 

 This band lias been well delineated by 

 Rolando, Reid, and others; it probably 

 forms a part of the cerebral fibres of the 

 medulla oblongata, and ascends through 

 the pons. 



The direction of the fibres of the restiform 

 bodies is longitudinal. Those which are 

 situate most posteriorly pass directly down- 

 wards, and are distinctly continuous with 

 the posterior columns of the spinal cord. 



Posterior view of the medulla oMonqata, u<ith mesocephale 

 and part of cerebellum of an infant. (After Foville.) 



S, pineal gland, 

 nates', 

 testes. 



+, point of emergence of fourth pair of nerves, 

 posterior pyramids. 



^, restit'onn columns. ,, -_i 



A, F, floor of the fourth ventricle, formed by the olivary The fibres which form the lateral and ante- 

 columns, the fissure between which is the calamus scrip- rior part of the restiform bodies pass down- 

 torius. wards and forwards to the antero-lateral co- 



Y', posterior_surface of mesocephale. lumns. A superficial groove, varying very 



much in distinctness in different subjects, 

 which passes upwards from the line of 



valve of Vieussens. 

 anterior surface of crus ccrebri. 

 R, corpus dcntatum or rhomboideum. 



