NEUROLOGY. Ill 



or horn of the grey matter. The anterior roots of the nerves are connected 

 with them, and the posterior roots adhere to them when the cord is split up 

 along the plane of the posterior horn. The posterior columns are small, 

 triangular in section, and placed in opposition with each other by their inner 

 surfaces. 



The spinal nerves. There is a pair of spinal nerves for each interverte- 

 bral foramen, and for that between the axis and occiput. There are thus 

 thirty-one pairs of nerves having their origin from the spinal cord, this 

 number being exclusive of the spinal accessory nerve, which is connected 

 with the upper part of the cervical region. Each spinal nerve has its origin 

 from the cord, by two roots, of which the anterior is distinctly inferior in 

 size to the posterior. The ligamentum articulatum (a narrow longitudinal 

 band on each side of the cord, and intervening between the dura mater and 

 the pia mater, attached to the latter by tooth-hke triangular processes) is 

 placed between these roots. Each root passes out through a distinct open- 

 ing in the dura mater. Immediately after its emergence a ganglion is 

 formed on each posterior root, and the anterior root lies imbedded in the 

 anterior surface of the ganglion, and involved in the same sheath, but with- 

 out mingling its fibres with those of the ganglion. Beyond it, the nervous 

 fibres of both roots intermingle, and a compound spinal nerve results. The 

 trunk thus formed passes immediately through the intervertebral tube, and 

 divides into an anterior (and usually larger) and a posterior branch, which 

 are distributed to the muscles and integument of the trunk and the extre- 

 mities. 



The anterior roots derive their fibres wholly from the antero-lateral 

 columns. Of these fibres, it is probable that some are continuous with the 

 longitudinal fibres of the cord, and that others pass into the grey matter. 

 The posterior roots adhere to the posterior part of the antero-lateral columns, 

 and derive their fibres chiefly from that source. It is probable, though by 

 no means certain, that the fibres of the posterior roots have a disposition 

 similar to that described for the anterior, and that while some pass into the 

 posterior horn of the grey matter, others are continuous with the longitudi- 

 nal fibres. 



In conclusion, the spinal cord may be said to be of a cylindroidal shape, 

 shghtly flattened on its anterior and posterior surfaces. At its inferior 

 extremity it gradually tapers to a point. In the cervical region there is a 

 swelling or enlargement, which begins a short distance beneath the medulla 

 oblongata, and gradually passes into the dorsal portion, which is the smallest 

 as well as the most cylindrical portion of the cord. This cervical enlarge- 

 ment begins opposite the third cervical vertebra, and ends about the third 

 dorsal. About the ninth or tenth dorsal vertebra, the lumbar swelling occurs, 

 occupying a space corresponding to about two vertebra3. The cervical 

 swelling corresponds to the point at which the nerves of the upper extremi- 

 ties are given off, and the lumbar has the same relation to the lower limbs. 



PL 137, fig. 3, spinal marrow and pons from the anterior surface : \ dura 

 mater; ''j ligamentum dentatum; ^'''^, single dentations of do.; \ a spinal 

 nerve. Fig. 4, a portion of the spinal marrow represented on a larger 



ICONOGKAPHIC ENCYCLOPAEDIA. — VOL. U. 52 817 



