11 



of arrangement visible even to the naked eye, they are found to be 

 connected with those on the inner layer of the skin. The presence 

 of these vessels is very remarkable, and serves to show that the sense 

 of vision of such animals must be far from perfect, for the rays of 

 light entering the eye must necessarily pass, first through these 

 vessels of the skin, and then those of the posterior layer of the cap- 

 sule, before they can fall upon the retina. It might be asked 

 whether such vessels exist in the Batrachian reptiles ; as far as my 

 experience goes, I have never yet been able to trace them. 



In the mammalian foetus, the vessels of the posterior layer of the 

 capsule are readily injected, but in the adult eye, except in cases of 

 disease, I have hitherto failed to fill them ; in the foetus, however, 

 they are of small size and very numerous, and in these animals we 

 may with ease often find that the anterior layer of the capsule is in- 

 jected as well as that of the posterior, and if the lens be removed 

 entire, it will be seen that the whole of its outer surface is covered 

 with vessels, but, as will presently be shown, the vessels of the two 

 layers differ materially both in size and arrangement. The vessels 

 of the posterior layer of the capsule of the foetal wolf, as shown in 

 Plate III. fig. 1, are of small size, they are derived from the arteria 

 centralis retina, which after reaching the capsule divides generally 

 into two branches, each of which divides and subdivides in a radi* 

 ating manner, so as to form a delicate plexus; on reaching the 

 equator of the lens, the vessels become more or less straight, and in 

 some cases, each straight vessel will split up into two branches, one 

 of which will pass into or join the vessels of the anterior layer of 

 the capsule, and the other anastomose with those of the iris* The 

 vessels of the anterior layer, as shown in Plate III. fig. 2, are of 

 much larger size and less numerous than those seen in fig. 1, which 

 is a representation of the posterior layer of the same lens, and they 

 evidently correspond in arrangement to those described as peculiar 

 to the membrana pupillaris, and as I have never been able to find 

 two sets of vessels in front of the capsule, it would appear that the 

 presence of a membrana pupillaris ; as generally described as filling up 

 or closing the aperture of the pupil, is more or less the result of ac- 

 cident : if the lens come away with its capsule entirely covered with 

 vessels, no membrana pupillaris will be found ; but if (as frequently 

 happens) the straight vessels above described as passing into the an- 



* Examples of the anastomosis of the vessels of both layers of the capsule, will 

 be seen in all the figures in Plates III. and IV. 



