G08 FUNCTIONS OF THE CEREBRO-SPINAL NERVOUS SYSTEM. 



Cord by a band of "arciform" fibres, whose connections were first distinctly 

 described by Mr. Solly; 1 of these there is a superficial set which unites 

 itself with the pyramidal columns, and a deep set which comes into relation 

 with the olivary. VI. The Posterior Pyramids are scarcely distinguishable 

 externally from the Restiform bodies, of which they were formerly described 



FIG. 214. 



FIG. 214. S.'ction made opposite First Pair of Cervical Nerves. The following references indicate the 

 same parts in Figs. 217-223 : a, anterior ; p, posterior root of Spinal Nerve ; i, ', anterior white column ; 

 o, posterior white column below, but in the higher sections restiform body ; 6 6, posterior pyramids; 

 e, gray Tubercle of Rolando; Hg, Hypoglossal Nerve; Sp. Ac., Spinal Accessory Nerve; V, Piieumo- 

 gastric Nerve ; yp, Glosso-pharyngeal Nerve. 



FIG. 215. Section passing through upper fibres of origin of First Pair of Cervical Nerves. 



FIG. 216. Section passing a quarter of an inch below Olivary bodies. 



as a constituent part; they form, however, the immediate boundaries of the 

 posterior median fissure; and whilst superficially marked off from the Resti- 

 form bodies by a slight groove, are more completely separated from them 

 by their anatomical relations to the parts above and below. Their fibres 

 establish a connection between the sensory tract (. t, s i) of the Crura Cere- 

 bri, and the posterior part of the lateral columns of the Spinal Cord, some 

 of them passing also into its posterior columns. These fibrous tracts are 

 stated by Mr. Solly 2 and Dr. Radclyffe Hall 3 to decussate, partially, at 

 least, whilst passing through the Pons Varolii. The arciform fibres (a/, 

 Fig. 212) here seen crossing the Medulla nearly at right angles, just below 

 the olivary bodies, which indeed they partly cover, have been shown by 

 Mr. J. L. Clarke to be only a superficial portion of a very important and 

 extensive order of commissural fibres (well seen in Figs. 217-219), the bulk 

 of which is much more deeply placed, and which not only connect the op- 

 posite halves of the Medulla Oblongata by traversing the raphe, but at the 

 same time form the means of communication between all the parts of each 

 separate half, the uetlike arrangement of the fibres being everywhere inter- 

 spersed with innumerable cells of varied shape and size, from which many 

 of the fibres may be seen to arise. The gradual development of the several 

 ((litres of gray substance in the Medulla Oblongata, and the relations which 

 they bear to the Cerebral nerves, most of which take their origin from this 

 part of the Spinal axis, may be rendered intelligible by a comparison of the 

 following diagrams. 



The first section here shown (Fig. 214) is made at the level of the lower 

 fibres of origin of the first Spinal nerves. On comparing the shape and 

 position of the gray substance with its appearance, as shown in Fig. 207, it 

 will be observed that the whole of the gray substance is here placed more 

 anteriorly in that section; that the posterior white columns (o and b) are 

 of large size, whilst the anterior and autero-lateral columns are compara- 



1 lMiilnso|)liic!il Transitions, 1836. * The Human Bruin, -M edit., p. 243. 



1 Kdinli. Mrd. nnd hurjj. Journ., July, 1847, plate vii. 



