1^79.] EYE-MUSCLES OF MAMMALS. 



127 



In the Lemures the choanoid appears again as a distinctly muscular 

 slip with the same relative attachment. 



Tlie superior oblique keeps its anterior position, the posterior 

 border being nearly twice as far from the optic nerve as the anterior 

 is from the cornea. 



The inferior oblique has also moved forwards, so that in Nycti- 

 cebus its posterior border is y\ from the optic nerve, while its anterior 

 IS /_ from the cornea. (In the Cebidse it is often five times nearer 

 to the optic nerve than it is to the cornea.) 



In Lemur some fibres of the superior oblique are inserted in front 

 of the superior rectus {so' in diagram). 



Tlie optic nerve is considerably to the inner side of the fundus. 



In Nycticebus there is a further peculiarity in the superior oblique, 

 in that it pierces the tendon of the superior rectus near its inner 

 border to be inserted behind it. 



Fig. 11. 



A diagram, from the outer side, of the eye of Nycticebus ■ shows that 

 the inferior oblique has moved further forward's. 



The following summary therefore appears to be true : 



a. In the higher Quadrumana the muscles closely resemble the 

 human muscles in their attachments, and, as was already known 

 there is no choanoid muscle. 



_ b. In the Cercopithecidae, besides other points of difference, there 

 IS always some representative of the choanoid. It is interesting to 

 observe that in the higher families the muscle which may be 

 supposed to be ceasing to be useful becomes degenerated and, at 

 last, almost unrecognizable. 



c. In the Cebidse no trace of choanoid remains, but the superior 

 oblique has moved forwards. 



d. In the Hapalidae the superior oblique has moved still further 

 forwards, and changed its relation to the superior rectus, while the 

 optic nerve has also moved outwards. 



e. In the Lemuridse the choanoid is again distinctly present, but 

 the superior oblique has a different relation to the superior rectus 

 and either pierces it or is attached partly in front of it, while the 

 inferior oblique is also moved forwards. 



