Ranson, Degeneration in Spinal Nerves. 275 



ward through the ligamentum nuchae until the tuberculum poste- 

 rius of the atlas was uncovered. The integument and long muscles 

 of the neck were held aside by a spring retractor inserted through 

 the median incision. The caudal margin of the atlas then served 

 as a guide to the point where the right second cervical nerve 

 emerges from the vertebral canal. A short stretch of the nerve' 

 was laid bare and cut with sharp scissors about i mm. from the 

 ganglion. No part of the nerve was resected and its central and 

 peripheral ends were held in close proximity by the mass of tissue 

 in which they were imbedded. 



All blunt dissection was avoided; sharp instruments were used 

 throughout, so that the tissues suffered a minimum amount of 

 injury. It was not practicable to close the wound with deep 

 sutures in the rats twelve days old, but this was done when the 

 operation was performed on adult rats. The skin incision was 

 closed with a collodion dressing. 



Were it not for the fact that a standard objection to results ob- 

 tained in this way is that they are due to a septic infection, the 

 reader might be spared the usual paragraph on asepsis. Under 

 the circumstances, however, some details must be given. The 

 skin of the animal's neck, after it had been freed from hair, was 

 thoroughly cleaned with ether-alcohol to remove oily deposits 



'Only the dorsal division of the nerve was cut; the ventral division, which is much smaller, was not 

 injured. This turns abruptly ventralward just distal to the spinal ganglion and was quite out of the 

 field of the operation. In order to form some idea of what proportion of the afferent fibers were severed 

 in cutting the dorsal ramus it is necessary to know the relative size of the two branches. In two cases 

 studied, the proportion of fibers was as follows: 



Specimen. Dorsal Remus. Ventral Ramus. Ratio. 



9 months, 302 gms. 2,402 887 1 12.7 



4 months, i6i gms. ^,39° 7o8 1:3.3 



The dorsal division is thus seen to be much the larger. It is mainly sensory since it forms the N. 

 occipitalis major, which, after giving off a few muscular twigs, goes to the skin on the back of the head. 

 The ventral division goes, in large part, to the muscles about its origin, only a small twig going to join 

 the common trunk of the N. auricularis magnus and N. cutaneus colli which, in the rat, is formed 

 chiefly by the ventral division of the third nerve. 



From these data we may roughly estimate that about 13 per cent, of the afferent fibers of the second 

 nerve go by way of the ventral branch and were not affected by the operation. This figure is obtained 

 by regarding the ventral branch as a purely muscular nerve, which according to Sherrington's ('94) 

 observations should be composed of afferent and efferent fibers in the ratio of 2 to 3. This would give 

 about 350 afferent fibers in the ventral branch, which, allowing for a 10 per cent, distal excess, would 

 leave 315 represented in the dorsal root. The average number of dorsal root fibers in these two nerves 

 was 2238, of which the 315 going to the ventral branch would constitute about 13 per cent. 



