10 DR. A. MILNES MARSHALL. 



The Development of the Cranial Nerves in the Chick. 

 By A. MiLNES Marshall, D.Sc.,B.A., Fellow of St. John's 

 College, Cambridge. (With Plates II and III.) 



I HAVE elsewhere shown^ that the mode of development of 

 the nerves, both cranial and spinal, of the chick is in all essential 

 points the same as that first described by Balfour- in the case 

 of the spinal nerves of Elasmobranchs, and subsequently ex- 

 tended by him so as to include the cranial nerves also.^ 



At the time of writing my previous account embryos of forty- 

 three hours were the earliest of which I had prepared satisfactory 

 specimens illustrating the development of the nerves, and I had 

 ^' not determined the exact date of the earliest appearance of the 

 nerves." * Since that time I have continued my investigations, 

 and have succeeded in preparing specimens illustrating the de- 

 velopment of both cranial and spinal nerves from their very 

 earliest appearance. 



In the present paper I propose, firstly, to describe these 

 earliest stages fully, so as to complete my previous account; 

 and, secondly, to give some further details concerning the mode 

 of development of several of the cranial nerves. I shall also 

 take the opportunity of correcting some statements in my former 

 paper that now appear to be wholly or in part erroneous. 



The majority of my specimens have been prepared by im- 

 mersion for three to five hours in Kleinenberg's preparation of 

 picric acid, and then transferring to alcohol of about 30 per 

 cent., which was gradually increased in strength till absolute ; 

 such specimens were subsequently stained with Kleinenberg's 

 solution of haematoxylin. I have also employed, with very 

 good results, weak solutions of chromic acid — \ to \ per cent. 

 — to which a few drops of a 1 p. c. solution of osmic acid were 

 added. In this solution the embryos were left for about twenty- 

 four hours, and then transferred to alcohol. They have the 

 advantage over picric acid specimens of not requiring staining ; 

 but are liable to become brittle and difficult to cut. 



The exceedingly close correspondence between specimens pre- 

 pared in these two ways is highly satisfactory as testimony of 

 their trustworthiness ; the correspondence being so close that 



' ' Proceedings of the Royal Society,' No. 179, 1S77 ; and ' Jonrnal of 

 Anatomy and Physiology', vol. xi, part iii, 1877. It is to the latter 

 paper, which contains a much fuller aescription, with figures, that I shall 

 refer in future. 



- ' Phil. Trans.,' vol. IGG, part i. 



3 'Journal of Anatomy and Physiology,' vol, xi, part iii. 1877. 



* Loc. cit., p. 504. 



