32 



BLIND VERTEBRATES AND THEIR EYES. 



The same elements are found over the eye that are evident in other regions. 

 There is no indication of a past free orbital rim; the dermis and epidermis are 

 directly continuous over the eye. There are no eye muscles and no glandular 

 structures connected with the eye. It is surrounded on all sides, except where it 

 becomes assoi iatcd with the skin, by loose connective tissue meshes filled with 

 fatty tissue, and is bound to the dermis by many fibers running in various directions, 

 and among these a few pigment cells are found. 



SCLERA AND CHOROID. 



(a) largest spi'diiii'ii* : Cartilaginous elements are found in the sclera of but 

 two eyes. Fn one individual, go mm. long, the left eye possesses a cartilage, while 

 there is none in the right eye. It is in this case placed just above the entrance of 



eft. 



e P. 



FIG. 4. Outline Sketch of Part of Section of Head of Specimen of Typhlomulgc ralhbuni, 

 QO mm. long, showing Position of Eye. 



the optic nerve and measures 96 /x in thickness, i6o/A vertically/and 204 p. antero- 

 |>o-teriorly. In all other cases the sclera is a thin, flocculent layer not distinctly 

 separable from the layers beneath it. It is thickest about the entrance of the optic 

 nerve. ( )vcr the front of the eye there are a few denser strands, which may repre- 

 -i 'lit the remains of the cornea. Over the sides of the eye of the largest individual 

 tin- sclera measures from 4 /a to nothing. About the entrance of the optic nerve it 

 attains a thickness of i \ /j., and contains many flat nuclei with a length up to 17 fi. 

 The ' horoid reaches a thickness of 20 /x near the entrance of the optic nerve, 

 and dwindles regularly from this point to the distal face of the eye. Blood-vessels 

 are lound in it nexl to ihe pigmeiited epithelium of the eye. Otherwise it is a 

 mass of pigment interlarded with streaks of colorless tissue containing nuclei. 

 < >\vr the Ironl of the eye, next to the epithelium, there are a number of colorless 

 cells with large, granular nuclei. 



ssentially the same conditions exist in younger specimens, but the parts are 



The ophthalmic artery, extending approximately parallel 



with the optic nerve during its di>tal course, is sometimes surrounded by pigment. 



