BLIND VERTEBRATES AND THEIR EYES. 



THE EYE MUSCLES. 



The eye muscles of 125 ft are well developed, with some anomalies in one of 

 the recti of each side. 



The two oblique muscles arise just below the point of exit of the olfactory nerve 

 from the brain cavity, downward and medial of the middle of the olfactory pit. 

 They are attached to the membrane connecting the ethmoid with the vomerine 

 cartilage. They extend backward in a canal bounded above by the ethmoid, 

 below by the vomer, and laterally by another cartilage. The upper oblique is 

 regularly horizontal-oval, measuring 34 fj. by 48 p.. The lower oblique is slightly 

 crescent-shaped in section with a diameter of 25/1 by 83 //,. These muscles are 

 attached on the sclera so that the tips of their insertion are just in contact with the 

 posterior rim of the scleral cartilage. The superior and inferior recti have their 

 points of insertion on the cartilage just outside the insertions of the oblique. 



The anterior rectus of the left side is inserted on the anterior face of the scleral 

 cartilage. It has a diameter of 20 \L near its insertion. It has its origin just in 

 front of the exit of the optic nerve. On the right side the muscle arises just below 

 the exit of the optic nerve, extends out and then curves down and joins the fibers 

 of the inferior rectus, following the fibers of this muscle and becoming indistin- 

 guishable from them. 



The posterior rectus arises far back, just below the origin of the ear capsule. 

 It extends out and forward, with a diameter of about 30 p, and attaches to the pos- 

 terior face of the eye. 



The superior and inferior rectus muscles are much stronger than the others; 

 they arise much farther forward than the posterior rectus, about on a plane con- 

 necting the posterior faces of the eyes. The upper rectus has a broad point of 

 origin, the inferior rectus a narrower one below it. The upper rectus curves upward, 

 forward, and out ; the lower runs in a nearly straight line obliquely down, out, and 

 forward. On both sides the upper rectus gives off fibers to the lower. The method 

 of the two sides is different ; on the right a compact bundle of fibers branches off 

 from the root of the muscle, passes toward the lower rectus to whose inner face 

 they become joined. The fibers pass from the origin of the superior to the in- 

 sertion of the inferior rectus. While some fibers seem to have a similar course on 

 the left, the conspicuous thing here is that fibers form an arch between the upper 

 and lower recti, their origin and insertion being both on the eye. The important 

 point is that in the eyes of the young the muscles, while varying to a degree on the 

 two sides, are all well developed. The muscles are still conspicuous in a specimen 

 97 mm. long, but in the mother of the young described and in older fishes, I have 

 not been able to find any muscles (plate 25, figs. E, F, G, msc.). 



THE SCLERA. 



The scleral cartilage is well developed at birth. Whereas, in Luclfuga, it formed 

 a partial shit-Id over the distal face of the eye, its pupilary diameter being much less 

 than the diameter of its proximal rim, it here forms a ring about the equator of the 

 eye the diameter of whose proximal rim is less than that of the distal opening. 

 The walls of the ring are thickest in front, where they reach 30 fi, tapering back- 

 ward. The ring in some cases fits the eye and does not, as in Lucifuga, suggest 



