310 



ginous, and which, on account of its being subject to compression 

 and concussion, does not contain any. 



Among the second class of extra- vascular tissues, the cornea is 

 first treated of ; and its structure is described as being very lax, and 

 as containing corpuscles only in a small quantity. The opinions in 

 favour of its vascularity are combated ; and it is shown that the 

 blood-vessels which converge to its attached margin, and which are 

 the principal source of the fluid that nourishes it, are large and nu- 

 merous, and that at the circumference of this tissue the arteries, 

 without any diminution of their calibre, return in their course, and 

 become continuous with the veins. A second set of vessels, devoted 

 to the nutrition of the cornea, is also described ; they extend to a 

 short distance over the surface of the tissue, but do not penetrate 

 into its substance. 



The crystalline lens is described as being composed of corpuscles, 

 of which the radiating fibres are constituted. The arteria centrahs 

 retinse is described as ramifying over the posterior surface of the 

 capsule, where it forms large branches ; these pass round the cir- 

 cumference of the lens, and reach its anterior surface, at the peri- 

 phery of which they become straight : the arteries terminate in loops 

 frequently dilated, and become continuous with the veins. With 

 respect to the vascularity of the vitreous humour, the author states 

 that although many anatomists have, in general terms, represented 

 the arteria centrahs retinse as giving off, in its course through this 

 organ, minute branches into its substance, stiU those who have paid 

 especial attention to the subject, have not been able to find such 

 vessels. He believes that the nutrition of this structure is accom- 

 plished by the fluid brought to its surface by the ciliary processes of 

 the choroid, which fluid is diffiised with facility through its entire 

 substance by means of the corpuscles of which its membrane is com- 

 posed, assisted by the semifluid character of the humour. 



The third class of extra-vascular tissues comprehends the epider- 

 moid appendages. The* author describes them all as composed of 

 corpuscles, which are round and soft where they are in contact with 

 the vascular chorion, compressed and flattened where they are farther 

 removed from it. He points out, in the substance of the hoof of 

 the Horse, the existence of fine canals, which he supposes to conduct 

 fluid through its mass ; and he states that the perspiratory ducts of 

 the human subject possess a structure analogous to the spiral vessels 

 of plants. The author describes each of the tissues of this class at 

 length, and shows that the various modifications presented by the 

 vascular system with which each is in contact, have the sole object 

 of enabling a large quantity of blood to approach and circulate 

 slowly around them. He also points out, in connexion with this 

 subject, the remarkable vital properties which are possessed by these 

 non-vascular tissues. 



In concluding this paper, the author states that his object has been 

 to establish as a law in animal physiology, that tissues are capable 

 of being nourished, and of increasing in size, without the presence 

 of blood-vessels within their substance. He shows the analogy 



