110 A. M. PATERSON. 



The present investigation has been undertaken with the 

 object of tracing the nerves in their development from the 

 condition in which previous embryologists have left them, to a 

 point at which they may be fairly compared with the adult 

 state. 



Chick embryos, artificially incubated, have been used for 

 the most part. By means of series of continuous sections, cut 

 in different directions, the nerves have been traced from end 

 to end in the different stages of development, from their first 

 appearance up to the formation of trunks having an arrange- 

 ment closely similar to that found in the adult. These sections 

 have been compared with sections of mammalian embryos of 

 different ages, with the result that the condition of develop- 

 ment of the nerves has been found to be identical in both at 

 periods in which the development of other parts and organs of 

 the body is the same. 



The methods adopted were in almost all cases the same. 

 For hardening the Mammalian embryos, Kleinenberg's solution 

 of picric acid was used ; for the Chick embryos, a cold saturated 

 solution of corrosive sublimate. A solution of borax carmine 

 was the staining agent employed, prepared according to 

 Balfour's directions. The sections were cut with a Jung's 

 microtome, fitted with an ordinary razor. 



The earliest stages in the development of the spinal nerves 

 in the Chick have been described by Marshall. He has shown 

 that they spring from the spinal cord as buds, of which the 

 dorsal are the first to appear, arising from the summit of the 

 cord. The more anterior of the dorsal roots arise from a 

 " neural ridge," an elevation continued back from the hind 

 brain. By the interstitial growth of the dorsal portion of the 

 spinal cord these roots become separated, and their attach- 

 ments to the cord more laterally placed. The ventral roots 

 appear at a later date. Projecting outwards directly, they 

 unite at an acute angle with the dorsal roots to form the 

 mixed nerve. The spinal ganglion on the dorsal root is 

 evident before the fusion of the two roots occurs ; it is formed 

 by the proliferation of the cells of the bud which form the 



