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 associated 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 specimens: Cartilaginous elements are found in the sclera of but 

 two eyes. In one individual, 90 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 



cps. 



Fig. 4. Outline Sketch of Part of Section of Head of Specimen of Typhlomulge rathbuni, 

 00 mm. long, showing Position of Eye. 



the optic nerve and measures 96 /x in thickness, 160 /j. vertically, and 204 ft antero- 

 posteriorly. 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. Over the front of the eye there are a few denser strands, which may repre- 

 sent the remains of the cornea. Over the sides of the eye of the largest individual 

 the sclera measures from 4 ^ to nothing. About the entrance of the optic nerve it 

 attains a thickness of 14 /*, and contains many flat nuclei with a length up to 17 ti. 



The choroid reaches a thickness of 20 /a near the entrance of the optic nerve, 

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

 are found in it next to the pigmented epithelium of the eye. Otherwise it is a 

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

 Over the front of the eye, next to the epithelium, there are a number of colorless 

 cells with large, granular nuclei. 



(b) Essentially the same conditions exist in younger specimens, but the parts are 

 relatively thinner. The ophthalmic artery, extending approximately parallel 

 with the optic nerve during its distal course, is sometimes surrounded by pigment. 



