792 THE SPINAL CORD. 



different intraspinal nerve paths. It seems likely that some afferent 

 root cells do lead into spinal paths of various functional quality, e.g. 

 into tactual, dolorific, and subconscious reilex. 



The axon of the afferent root cell sometimes gives a " side-fibre " near its 

 origin which recurves to apply itself to the perikaryon. 1 



In all the spinal nerves the ascending stems from the afferent fibres seem 

 to he longer than the descending, but in the case of some of the cranial nerves, 

 e.g. trigeminus, the descending are the longer. In each of the spinal nerves 

 the ascending stems from certain of the root cells pass to the dorsal column 

 nuclei of the bulb ; thus, from the lowest nerves, these ascending stems extend 

 through the whole length of the spinal cord. What proportion of the root 

 cells of any particular afferent root possess, by means of long ascending stems, 

 direct connection with the bulbar nuclei, is not known ; the large afferent 

 roots belonging to the limbs seem to furnish a larger number than the small 

 afferent roots of other regions. The total region of embouchment of any one 

 afferent root in the cord is therefore wide. It extends from probably a couple 

 of spinal segments behind the surface attachment of the root anteriorly to the 

 bulb itself. 



It appears pretty certain that in front of (above) the segments composing the 

 particular region abutting on the segment to which the ganglion of the root 

 belongs, the ascending stem passes most of the segments without sending 

 collaterals into them, and unconnected with them enters the dorsal nuclei of 

 the bulb. Nine collaterals have been counted from one root fibre in the 

 funiculus cuneatus. v. Lenhossck has not found any collaterals to fibres in the 

 funiculus gracilis. 



When, after transection of the bulb close to the calamus scriptorhis, the 

 extreme top of the dorso-median column is faradised,- movements of the 

 homonymous leg are evoked ; in the monkey, movements of the foot. 

 When the mesial part of the extreme top of the dorso-lateral column is 

 similarly stimulated, movements of the homonymous hand result. In the 

 same way, from the top of the dorso-mesial column, movement over the 

 lowest intercostal spaces can be evoked. These movements appear to be 

 reflexes, involving antidrome conduction down the ascending stems, and 

 so, vid collaterals given off near the entrance of the root cell fibres, into 

 the cord. The reactions indicate that the long ascending fibres are 

 given off by thoracic as well as by limb roots, and that under the 

 circumstances the collaterals by which reflexes are particularly facile are 

 those given off by the stem fibres near the entrance of the root into the 

 cord. 



The date at which a nerve fibre completes its development, by acquiring a 

 myelin sheath, 3 indicates the time at Avhich it becomes functionally active. 

 The long ascending stems (fun. gracilis) of the afferent root cells do not become 

 myelinate 4 until much later than the medium and short fibres, except of 

 Lissauer's marginal zone. The long ascending fibres would therefore pertain 

 to a system characterising a more highly developed phase of existence than 

 do the short intraspinal. The long ascending stems form, however, a very Avell- 

 developed spinal column in systems even as low as that of the frog. 



Besides the dorsal column nuclei of the bulb, the " column of Clarke " 

 forms a nucleus of ending for many of the collaterals from ascending stems 

 of afferent root cells in the lumbo-sacral region. And the lateral division of 



1 C. Huber, Anat. Anz., Jena, Bd. xii.; J. Dogiel, ibid., 1896. 



2 Sherrington, Proc. Roy. Soc. London, 1897. 



3 Flechsig, in C. Ludwig's laboratory, Leipzig, 1875 ; for latest extensions of method, 

 see Ambronn & Held, Arch.f. Physiol., Leipzig, 1896, S. 202. 



4 Flechsig, op. cit., and especially Trepinski, Arch.f. Psychiat., Berlin, Bd. xxx. S. 54. 



