THE EYES OF AMBLYOPSIS. 137 



extends from the inferior oblique horizontally backward, taking its origin with the 

 rectus muscles. This muscle in its posterior extent has the characteristics of the 

 inner rectus. But whether or not its fibers reach the eye, I was unable to determine. 

 If they do, they reach it with the fibers of the lower oblique. 



The rectus muscles arise from the lateral margin of the bone forming the brain 

 case, just behind the anterior end of the brain, the upper rectus taking its origin 

 behind the others. They extend as four bundles forward in a connective tissue 

 tube. Before leaving this tube they are reduced to three bundles by the union 

 of a small bundle situated above the others in the tube with the largest bundle 

 situated nearest the outer margin. One of these is the lower rectus. The largest 

 one is the upper rectus and the one joining it, in all probability, the external rectus. 

 The external rectus, if I am correct in the identification, is not distinguishable from 

 the latter during the rest of its course nor in its insertion in the sclera. The entrance 

 of the rectus muscles into the connective tissue sheath occurs 0.5 mm. behind their 

 insertion in the eye. In this eye we have the two oblique muscles, the upper rectus, 

 the lower rectus, a small bundle of fibers following for the most part the course 

 of the upper rectus, the external rectus, and a small bundle of fibers extending from 

 the origin of the rectus muscles forward to the lower oblique which may be the 

 inner rectus. We have at least five, probably all six, of the muscles normal to fish 

 eyes. But that this is not always the case is very strikingly emphasized by the fact 

 that the eye of the opposite side of the same individual lacks the upper oblique. 



In another individual the superior rectus and superior oblique are the only 

 muscles present on the left, while on the right the upper rectus is the only muscle 

 present. The preparations of this individual are particularly favorable for tracing 

 the muscles. They are stained with Mayer's haemalum and indigo carmine. The 

 muscles are stained an intense blue, while the connective tissue through which they 

 pass is light purple. 



In still another specimen both the oblique muscles are present on the left and 

 three of the rectus muscles, one of which, the interior, extends forward in the inner 

 part of the orbit and joins the lower oblique as in the first individual described. 

 No fibers of this muscle reach the eye. On the right side of the same individual 

 the upper rectus and but one oblique muscle are present. In still other individuals 

 not suitable for tracing the muscles, their fluctuating number has been noted, and 

 their varying method of attachment to the eye is also a matter frequently noticed. 



Inside of the loose connective tissue surrounding the eyes there is a more compact 

 sheath. This is thickest in front of the eye where it contains spherical nuclei and 

 holds one to three compact cartilages which usually are disposed to form a hood 

 over the front of the eye. These cartilages, described by Wyman in this species 

 and by Kohl in rosce, and taken by the latter as the remnants of suborbital bones, 

 have nothing whatever to do with the latter structures. Their nature can be under- 

 stood from their close association with the eye, by the fact that they are closely 

 bound together by the scleral connective tissue, and by the fact that some, at least, 

 of the eye muscles are attached to their outer surfaces. They are unquestionably 

 scleral elements (scl.c. in figs. 49 to 52). There may be some hesitation in accepting 

 this view of the nature of these cartilages since no cartilage whatever is found in the 

 sclera of Chologaster. Their position, usually in front of the eye, is also anomalous 

 if they are scleral cartilages. It may be stated, however, that the eye of Amblyopsis 



