ROOTS OF THE SPIXAL NERVES. 



277 



ganglia (fjanfjlici nlx-rrantin of Hyrbl) are sometimes found on the posterior roots of the upper 

 cervical nerves. The ganglia of the lumbar and upper sacral nerves are often double, there 

 being- a distinct swelling on each of the bundles of the posterior root. The ganglion of the 

 suboccipital nerve may be situated within the dural sheath, or be wanting (9 per cent. r 

 Kazzander). but in such cases there are probably nerve-cells interspersed in the posterior root. 

 According to Rattone there are regularly scattered nerve-cells along the posterior roots of all 

 the spinal nerves (Internat. Monatschr. f. Anat. u. Hist., i, 1884). 



Size. The roots of the upper cervical nerves are smaller than those of the lower 

 nerves, the first being much the smallest, and the sixth the largest. The posterior 

 roots of these nerves, with the exception of the first in which the anterior root is 

 larger than the posterior, exceed the anterior in size more than in the other spinal 

 nerves, and they are likewise composed of filaments which are considerably larger 

 than those of the anterior roots. 



The roots of the dorsal nerves, exception being made of the first, which resembles 

 the lowest cervical nerves and is associated with them in a part of its distribution, 

 are of small size, and vary but slightly, or not at all, from the second to the last. 

 The filaments of both roots are thinly strewed over the spinal cord, and are slender, 

 those of the posterior exceeding"] in thickness those of the anterior root in only a 

 small degree. 



The roots of the lower lumbar, and of the upper sacral nerves, are the largest of 

 all the spinal nerves ; those of the lowest sacral and of the coccygeal nerve are, on 

 the other hand, the smallest. All these nerves are crowded together upon the 

 lower end of the cord. Of these nerves the anterior roots are the smaller, but the 

 disproportion between the anterior and posterior roots is not so great as in the 

 cervical nerves. 



Length. The place at which the roots of the upper cervical nerves are 

 connected with the spinal cord being nearly opposite the foramina by which they 

 respectively leave the canal, these roots are comparatively short. But the distance 

 between the two points referred to is gradually augmented from nerve to nerve 

 downwards, so that the place of origin of the lower cervical nerves is the depth of 

 at least one vertebra, and that of the lower dorsal nerves about the depth of three 

 vertebrse, above the foramina by which they respectively emerge from the canal. 

 Moreover, as the spinal cord extends no farther than the first lumbar vertebra, the 

 length of the roots of the lumbar, sacral and coccygeal nerves increases rapidly 

 from nerve to nerve, and in each case may be estimated by the distance of the 

 foramen of exit from the extremity of the cord. Owing to their length, and the 

 appearance they present in connection with the spinal cord, the aggregation of the 

 roots of the nerves last referred to has been named the cauda equina. 



A. diagram showing the level at which the several roots arise from the cord in relation to 

 the spines of the vertebrae, as determined by R. W. Reid, is given on p. 4 of Part I. of this 

 volume. The absolute length of certain of the nerve-roots in a subject of 18 years of age. 

 whose spinal cord was 41 cm. long, is shown in the following table, taken from Testut : 



