334 ANATOMY OF THE OENTKAL NEHTOUS SYSTEM. 



Between the spinal ganglion and the spinal cord both the sensory and 

 the motor roots break up into smaller fasciculi, — "root-fibers/' — which enter 

 the cord at considerably various levels, the sensory fibers posteriorly, the 

 motor ones anteriorly, each in a somewhat laterally placed longitudinal 

 sulcus. The number of these fasciculi is not the same for different roots, 

 and varies also in different individuals. 



Eecent investigations have shown that for the extremities not every 

 spinal root is in relation to a particular peripheral nerve. It is established 

 that in every nerve going to one of the extremities, are contained a large 

 number of fibers coming from different spinal roots, and it is very probable 

 that two muscles, functioning usually co-ordinately, are innervated from 

 the same root, even when supplied by different nerves. The apportionment 

 of fibers, which renders this possible, takes place partly in the plexuses (cer- 

 vical, lumbar, etc.), and in part in the trunks of the larger nerves, which 

 may themselves be regarded as a kind of plexus. 



Only a, few eases of disease of the spinal ganglia are reported. Besides ex- 

 treme pain, an intercostal herpes zoster in the course of the respective nerve was 

 repeatedly observed. Physiological observations (Gaule) indicate that vasomotor and 

 trophic influences on the skin and muscles are the province of some of the cells in 

 the spinal ganglia. Perhaps, in this connection, the sympathetic fibers, which sur- 

 round the cells abundantly, come into consideration. It must not be overlooked, how- 

 ever, that we know of marked changes occurring in the spinal ganglia in tabes (Vul- 

 pian, Wollenberg, and others) which have been unaccompanied by herpes or any- 

 thing related to it. 



The roots enter the cord in longitudinal rows. 



Where large roots, corresponding to the extremities, enter the cord, 

 the latter is greater in size than elsewhere. The intumescentia cervicalis 

 receives and gives off the arm-nerves; the intumescentia lumbalis, the leg- 

 nerves. The smallest portion of the cord emits the intercostal nerves. The 

 lowest, conical portion of the cord is called conus terminalis; from it arises, 

 in addition to the nerves, a long, thin process, the filum terminale. The 

 superior boundary is the beginning decussation of the pyramidal fibers (see 

 below). 



In examinations of patients the important question often arises, from what 

 level of the cord emerge the particular spinal roots supplying paralyzed muscles or 

 ansesthetic areas of the skin. It has been sought to solve this question by experi- 

 ments on animals, than i\'hich anatomy itself could not serve the purpose better. 

 With man it has been repeatedly sought to derive more knowledge on this point 

 from cases of localized lesions of the cord (contusions, hemorrhages, etc.). Follow- 

 ing is a list, slightly modified, taken from a compilation of all accessible reports of 

 cases up to 1890, made by Starr. Probably e.xperienee will dictate changes here and 

 there. 



