1^79.] EYE-MUSCLES OF MAMMALS. 123 



bined, not with the inferior, but with the superior rectus ; and the 

 same disposition is found in all the Reptiles and Birds that I have 

 examined. Not only so, but ia some Mammalia, particularlj those 

 in which the eyes aie placed at the side of the head, as in the Rodents 

 and others, the muscles must be combined as they are in the fish 

 or bird. 



Professor Struthers, in a paper on the action of the oblique muscles 

 (Monthly J. of Med. Science, Oct. 1849), has already drawn attention 

 to the differences in the direction of these muscles which are found 

 ill the Mammalia, and has pointed out that the more the eyes are 

 directed outwards, the more does the angle which the superior oblique 

 makes with the visual axis tend to become acute. 



The accompanying diagrams will explain this change in the anHe. 



Fig. 1 re{)resents the visual axes VA VA' parallel as in man ; 

 SO SO' the direction of the superior oblique; the angle S c A is 

 obtuse. In fig. 2 the axes are divergent, as in the Rabbit : the 

 letters correspond ; the angle S c A is acute. It will be noticed also 

 that SO 80' are directed to the front of the eye instead of to the 

 back. This forward position of the superior oblique muscle, how- 

 ever, as will be jjresently shown, is not peculiar to those animals in 

 which the eyes diverge. 



Among the Quadrumana I have examined the attachment of the 

 eye-muscles in the following genera and species : — 



Fam. Simiidse. — -Sitnia sati/riis. 



Fam. CercopithecidiE. — Semnopithecus leucoprymnus, Cercopi- 

 thecus calliirichus, C. alblyularis, Cercocebus fuliginosus, Macacus 

 inuus, Cynocephalus porcoriiis. 



Fam. Cebidae. — Ateles ater and A. melanochir, Mycetes seniculus, 

 Cebus capucinus, C. hypoleucus, Nyctipithecus felinus, Saimaris 

 sciurea. 



Fam. Hapalidse. — Hapale penicillata, Midas rosa/ia. 



And in the Lemures, fam. Lemuridse, Lemur, sp.?; fam. Nycti- 

 cebidse, Nycticebus tardigradus. 



In the human eye my observations agree with Sappey's description 

 rather than with that of Henle ; and I therefore give the measurements 

 to be found in Sappey's ' Anatomic Descriptive,' and a diagram, to 

 serve as a standard of reference. 



The superior rectus is inserted -^-^ inch from corneal edge. It is 

 curved ; and its outer is further from the cornea than is its inner edge. 



The inferior rectus at a distance of ^. (It is also obhque like 

 the superior.) 



The external rectus -^-^. 



The internal or median rectus -^-^ to -^-s;. 



The superior oblique ^ (I should rather say -^-^ from the optic 

 nerve. 



The inferior oblique ^^ from the nerve-entrance. The line of its 

 insertion, if prolonged, would meet the optic nerve. 



Neither of these authors refers to the curvature of the line of in- 

 sertion of the superior oblique. 



In Simia satyrus it will be seen that the attachments resemble 



