OF NON-VASCULAR ANIMAL TISSUES. 185 



especial attention to this subject, and has examined injections of inflamed eyes, says, 

 " I have not seen any injected vessels in the vitreous body ;" and adds, " I do not 

 despair of seeing this part also injected*." 



Since the above was written, I have met with the following account of an injection 

 of the membrane surrounding the vitreous body : — " Mr. Dalrymple has succeeded in 

 injecting a number of minute ramifications, of very delicate vessels, on the periphery 

 of the membrane (of the vitreous body) derived from a branch or branches of the 

 central artery, which passed by the spot termed the foramen of Soemmering ; he 

 kindly permitted me to inspect the preparation, which was most satisfactory, but 

 which I much regret has been since destroyed by accident -{-." 



My researches induce me to believe that the vessels of the vascular ciliary processes 

 of the choroid membrane, to which no specific function has hitherto been given, have 

 the function of nourishing the vitreous body. My opinion is confirmed by that of 

 MiJLLER, who says, " The zonula Zinni, or corona ciliaris, appears from Henle's and 

 Schroeder's injections, to be a vascular organ, and to be of great importance for the 

 nourishment of the transparent humours J." 



I have succeeded in making very minute injections of the vessels of the ciliary 

 processes, the disposition of which is remarkably beautiful ; they have been most 

 accurately delineated and described by Zinn. I have particularly to allude to the 

 immense quantity of blood that their large size allows to be continually circulating 

 through them, and to their plexiform character, which is productive of a slow cir- 

 culation of the fluid they carry. At the free border of each ciliary process is a large 

 single vessel, which is received into the base of the sulcus of the vitreous humour, 

 and is in immediate contact with it. When it is remembered that the investing 

 membrane of the vitreous humour is very delicate, and that it is made up of cells or 

 corpuscles, and that it has in immediate contact with its free surface these large 

 and numerous vessels, they may perhaps with great reason be considered as the 

 organs of nutrition of the vitreous humour, by eliminating a nutrient fluid which pe- 

 netrates into, and is diflfused through, the substance of the latter. 



The Third Class of Non-vascular Animal Tissues. 



Of the Epithelium^ the Epidermis^ Nails and Claws, Hoofs of various hinds, Hair and 



Bristles, Feathers, Horn and Teeth. 



The above structures are placed together as forming a distinct class of extra vascu- 

 lar tissues, on account of their being all developed upon the surface of the chorion, 

 and very analogous to each other in their structure, their mode of growth and 



* Muller's Elements of Physiology by Baly, vol. i. p. 216. 



t A practical work on the Diseases of the Eye, by F. Tyrrell, p. 97. 



X Loc. cit.,p. 219. 



