1879.] EYE-MUSCLES OF MAMMALS. 125 



There is no choauoid muscle'; and the obliquity of the inferior 

 oblique is remarkable. 



In all the Cercopithecidge, as, indeed, in all the Old-World Mon- 

 keys below the Simiidse, there is a representative of the choanoid 

 muscle, in the shape of a larger or smaller muscular slip, inserted 

 between the superior and inferior oblique. In Semmpithecus leuco- 

 prymnus this slip was very small, the fibres were fattily degenerated, 

 and no strise were perceptible ; but, at the same time, the atrophied 

 remains were distinctly recognizable. In Cercopithecus callitrichus 

 the muscle was even less distinct ; there was nothing but a thin 

 fibrous sheet, quite isolated from the capsule enclosing the sclerotic, 

 it is true, and with an insertion corresponding to that of the choanoid 

 sHpiu other members of this group; but microscopically no muscular 

 fibres were found, only vessels and fibrous tissue remained. 



In C. alhicjiduris the slip was larger and contained distinctly 

 striated muscular fibre, as also in Gercocebm fuliginosus. In Ma- 

 cacus innuus and Ci/nocephalus jjorcarius this muscular band was 

 larger and veiy evident. 



The differences between these members of the group vfith respect 



Fi2. 7. 



A diagram of the attachments in Macacus innuus, from above and outside • 

 shows the relative positions of the oblique muscles to one another and to 

 the choanoid. 



to the other muscles were slight. In all, the outer borders of the 

 superior and inferior recti were posterior to the inner borders, while 

 the median rectus was slightly nearer to the cornea than the ex- 

 ternal (as a rule). 



In all, the anterior edge of the superior obhque was more distant 

 from the cornea than was the posterior from the optic nerve, while 

 the inferior oblique remained near the back of the eye. The optic- 

 nerve entrance was always internal to the visual axis. 



In the Cebidse and Hapalidse we have an important difference. 

 The choanoid slip is entirely absent ; even in the Marmosets I could 



' This muscle, very seldom absent in the Mammalia, arises on the outer side 

 of the optic nerve, is inserted into the sclerotic behind the recti, and is supplied 

 by the sixth nerve; but its size and its attachment to the sclerotic varv much. 



