762 SPECIAL HISTOLOGY. 



and another, external and posterior, extending backwards from the 

 same points upon the border of the lejis — the memhrana capsulo-pupil- 

 aris. The latter becomes more and more distinct as the lens and 

 aqueous chambers are developed and the lens retreats, until at last it 

 represents a delicate membrane stretching across the posterior chamber. 

 The venous blood from all these parts is returned through the veins of 

 the iris, and from the outer surface of the vitreous body, also through 

 those of the retina, and perhaps through a vena hyaloidea, said to take 

 the same course as the artery, but of the existence of which many 

 authors doubt, and which I have never myself seen. With respect to 

 the genetic import of the vascular capsule, nothing has as yet been 

 ascertained. I find it to be composed of a homogeneous tissue, with a 

 few scattered cells, and regard it as a structure corresponding to the 

 cutis, which, in the formation of the lens, is detached from the skin, 

 together with a portion of the epidermis, and remains in the eye. The 

 vitreous body, then, may be understood as modified subcutaneous con- 

 nective tissue, — a supposition not at all incongruous with the observations 

 above adduced, and the more so, because, as I have shown (§ 24), all 

 the subcutaneous connective tissue of the foetus is at one time perfectly 

 gelatinous, and, like the enamel organ which also belongs to the same 

 tissue in specie, strikingly resembles the vitreous body in aspect and 

 consistence. 



Concerning the histological development of the eyes, the following 

 only need be remarked. At an early period they consist in all their 

 parts of formative cells of uniform size, which, in process of time, are 

 metamorphosed into the various tissues. In the fibrous coat, in the 

 second and third month, the cells are developed, in the mode already 

 described (§ 24), into connective tissue, and at the same time the dis- 

 tinction is set up between the cornea and sclerotic, which are at first, 

 externally, exactly alike, and constitute only a single membrane. In 

 the uvea the cells are for the most part employed in the formation of 

 vessels ; another portion goes to the formation of the inner and outer 

 pigment-layers, pigment-granules being deposited in them at the com- 

 mencement of the third month, whilst another is transformed into 

 muscles, nerves, the epithelia and connective tissue of these membranes. 

 The development of the nerve-cells and of the so-termed " granules" 

 from embryonic cells, may be readily traced. I have observed the 

 same thing also with respect to the "cones;" and I think that, in the 

 Frog, it may be assumed with respect to the " rods" likewise, that they 

 are nothing but elongated cells ; whilst in the Mammalia, the formation 

 of the "rods," and of the nerve-fibres themselves, has not yet been 

 traced. The lens, lastly, is originally composed entirely of cells, 

 which, in course of time, are transformed into the tubes. The precise 

 nature of the processes attending these changes has not yet been 



