﻿EYE OF LUCirUGA. 213 



level of the optic nerve. The former retains its distinct cartilaginous nature while 

 the latter has lost it to such an extent that it is only by inference that it can be 

 considered of cartilaginous origin. These are the only cartilages seen in eyes of 

 individuals over 40 mm. long. The fibrous part of the sclera is as well developed 

 as in the younger eyes, and indeed near the nodules of cartilage in the left eye it 

 is distinctly thicker than in the younger stages. The sclera as a whole no longer 

 forms a capsule much larger than the eye ; it fits snugly against the eyeball, except 

 in the cornea of the right eye, where it forms an arch over the iris and pupil in the 

 normal way. Where the cornea joins the sclera proper in the right eye, there is 

 again a material thickening of tissues. 



The cornea in older individuals undergoes many modifications. It retains 

 its shape for but a short time after birth. In 16 individuals over 24 mm. long it 

 retained its original outline in only 4 eyes in 4 different individuals, one 28 mm. 

 (plate 20, fig. a), one 38 mm., one 53 mm., and one 65 mm. long (plate 21, fig. a), 

 the mother mentioned above. In the other eyes the aqueous space is obliterated, 

 and the cornea more or less disintegrated. In cases where the vitreous cavity had 

 disappeared, and the pupil had become closed, the cornea was at times replaced 

 by a lenticular mass, cellular rather than fibrous (plate 20, fig. c). 



The points of interest are that the sclera develops early and on a scale much 

 beyond the present needs of the eye, i.e., it preserves a past phylogenetic stage far 

 better than the other parts of the eye, and yet ontogenetically it degenerates much 

 more rapidly than any other part, with the possible exception of the lens. 



THE CHOROID AND RETINAL BLOOD-VESSELS. 



In unborn young about 20 mm. long there is considerable space between the 

 sclera and choroid. At first sight this may be taken as the result of shrinkage on 

 the application of reagents, but a closer inspection shows the space to be filled with 

 an undisturbed gelatinous substance interspersed with nuclei. It represents the 

 suprachoroid al lymph space. Immediately in contact with the eye, the gelatinous 

 matrix is replaced by fibers. The normal condition of the gelatinous layer is 

 further testified to by the dendritic choroidal pigment cells that are scattered through 

 it and occasionally are arranged into a thin layer, dividing the mass into approxi- 

 mately two equal layers. Still further evidence is given by the occasional blood- 

 vessels passing tlirough it. 



In 76 a there is a fine capillary meshwork in the choroid. In the meridian of 

 the optic nerve an artery approaches the entrance of the optic nerve from below 

 and a vein much thicker leaves it above. The vein is made up of two branches in 

 the choroid near the entrance of the optic nerve, one branch coming from above, 

 the other from below. The artery enters the retina along the lower edge of the 

 optic nerve. The vein leaves the retina in this eye over the lower margin of the 

 iris. The meshwork of blood-vessels over the inner surface of the retina contains 

 many far beyond capillary size, closely approaching in thickness the retina itself. 

 There is a median vessel extending from the lower edge of the pupil along the sur- 

 face of the retina up to a level with the upper surface of the lens. 



In the left eye of 76 the ophthalmic vein measures 50 /a in diameter, while the eye 

 itself measures but 170 /a. In the eyes of this individual I have not been able 

 to make out any blood corpuscles, nor have I been able to identify the ophthalmic 

 artery. 



