112 BLIND VERTEBRATES AND THEIR EYES. 



The 6 normal eye muscles are present in Chologaster. The 4 rectus muscles 

 arise near a common point just behind the point of exit of the optic nerve from the 

 skull. The M. rectus superior passes from this point outward, upward, and for- 

 ward. The M. rectus inferior passes nearly horizontally outward and forward. 

 The M. rectus externus passes nearly straight out at right angles to the axis of the 

 body to the posterior face of the bulb. The M. rectus internus is probably the 

 longest, passing outward and forward to the anterior face of the eye. 



The two oblique muscles originate near a common point well in front of the 

 exit of the optic nerve and are inserted near the insertion of the M. rectus superior 

 and inferior. There is nothing remarkable about any of these muscles and they 

 are mentioned solely as a basis of comparison with the condition found in Ambly- 

 opsis. The space from the wall of the brain case outward about the eye muscles 

 and eye is bounded by a connective tissue capsule. Within this capsule, the space 

 between the muscles and the posterior part of the optic pit and the eye is filled with 

 fat. Above this capsule lies another mass of fat and below it still another (fig. 35 b). 

 The- supraorbital does not help to protect the eye, which lies entirely lateral from 

 it and extends above it. The suborbital bones are thin, hollowed sheets of bone 

 backing the suborbital mucous canal. Their number, etc., has not been deter- 

 mined, but their location is of importance in view of a statement made by Kohl 

 concerning their absence in Troglichthys. 



The sclera is represented by a thin fibrous capsule which is sometimes widely 

 separated from the eye by reagents. In the largest specimen it is but 4 ^ thick. It 

 is continued over the front of the eye in contact with the dermis as a thin cornea 

 (fig. 35 a). This is much more compact than the rest of the sclera. It readily 

 separates from the dermis. The sclera is never at any place cartilaginous. I 

 was at some trouble to demonstrate the absence of cartilage, even in the largest 

 specimen, in order to detect if possible the homologues of the cartilages in Ambly- 

 opsis and Troglichthys rosa, and can state positively that no cartilage is found 

 associated with the eye of Chologaster papilliferus or in fact with the eye of any of 

 the species of Chologaster. 



The choroid is very thin. Just within the sclera is a homogeneous, sometimes 

 excessively thin, layer containing a few nuclei, the suprachoroidal lymph space. 

 If the eye contracts through reagents, the choroid which clings to the eyeball is 

 separated from the sclera by the widening of this space. Pigment is not abundant 

 except over the iris and below and at the sides of the entrance of the optic nerve. 

 About the entrance of the optic nerve a mass of pigment is prominent, being espe- 

 cially conspicuous in the largest specimen (fig. 35 c). A mass of pigment which 

 may be homologous with this has been described by Ritter in Typhlogobiiis, who 

 found no cellular structure in the pigmented mass in Typhlogobiiis and identified 

 tliis | lamented mass as the choroid gland. A choroid gland or the rete mirabile is 

 not found. A processus falciformis is not present. Blood-vessels are not numer- 

 ous and it was impossible to separate a distinct vascular layer of the choroid. In 

 the largest specimen the choroid is much richer in blood-vessels ventral of the 

 pigmented mass at the entrance of the optic nerve than elsewhere. The capillary 

 l;iyer reaches here a total of Q /^ in thickness. A layer of excessively thin pigment 

 cells lies close to the pigmented layer of the retina. It is so thin and so closely 

 applied to the pigmented layer of the retina that it is only in a few tangential sections 

 that this part of the choroid becomes evident. 



