OP NON-VASCULAR ANIMAL TISSUES. 183 



2. The Crystalline Lens. 



Of the Structure of the Crystalline Lens. — According to the researches of M. 

 Schwann, the crystalline lens, in the earliest periods of its development, is entirely 

 composed of cells ; and it is the opinion of Valentin and himself, that these cells 

 are converted into the fibres of the lens. The dentations of the fibres of the lens 

 are compared by M. Schwann to the sinuosities of a not uncommon form of vegetable 

 cells*. 



In the examinations that I have made of the crystalline lens, I have not only found 

 cells interspersed among its fibres, but have frequently seen the fibres themselves, 

 composing the external part of the lens, made up of these cells ; and in other in- 

 stances they occupy the margin of the fibres only. 



Of the Blood-vessels which nourish the Crystalline Lens. — The crystalline lens, in a 

 healthy state, has never been seen to contain blood-vessels. Muller, in speaking 

 of the mode of development of this organ, says, " The matrix of the crystalline lens is 

 its capsule, which seems to secrete the layers of the crystalline from its inner surface." 

 The presence of vessels in its substance would certainly interfere with the functions 

 of the crystalline lens ; for, as I have said, perfect transparency is essential to its 

 office of transmitting light. In the anterior capsule, according to Muller, " the 

 vessels are extremely difficult to inject ;" he however states that " in inflamed eyes 

 they are distinct, both on the anterior and posterior walls of the capsule." The pre- 

 sence of blood-vessels in the anterior capsule of the lens would as effectually derange 

 the functions of the eye, as if they were in the substance of the cornea, or in the lens 

 itself. 



I have not only been unable to trace vessels into the anterior capsule, but I hope 

 to prove that in the healthy state no vessels do enter it. The posterior capsule of the 

 lens is, however, injected with facility, and contains large and numerous ramifications 

 of blood-vessels ; I ascribe to them the function of supplying the crystalline lens with 

 a nutrient fluid. These vessels arise from the arteria centralis retinae ; the latter, 

 having traversed the centre of the vitreous humour, expands upon the capsule, and 

 forms the ramifications just noticed. Now in some injections which I have made of 

 the eyes of a human foetus, of the sixth or seventh month, these vessels were not 

 confined to the posterior surface of the capsule ; they pass round its border and 

 extend upon its anterior face to the extent of one quarter of a line. I have not been 

 able to make a perfect injection of the vessels of the capsule of the lens in ages 

 antecedent to the fifth or sixth month of the foetal life, and therefore am unable 

 to say whether in the very early periods of development, the anterior capsule, like the 

 membrana pupillaris, is entirely traversed by vessels; the crystalline lens would, 

 under such circumstances, be completely surrounded by blood-vessels. 



The branches of the arteria centralis retinae in the early periods of life, as noticed 



* British and Foreign Medical Review, vol. ix. p. 512. 



