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Show 1879.] EYE-MUSCLES OF MAMMALS. 125 There is no choanoid muscle1; and the obliquity of the inferior oblique is remarkable. In all the Cercopithecidae, as, indeed, in all the Old-World Monkeys below the Simiidae, 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 Semnopithecus leuco-prymnus this slip was very small, the fibres were fattily degenerated, and no striae 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 slip in other members of this group; but microscopically no muscular fibres were found, only vessels and fibrous tissue remained. In C. albigularis the slip was larger and contained distinctly striated muscular fibre, as also in Cercocebus fuliginosus. In Macacus innuus and Cynocephalus porcarius this muscular band was larger and very evident. The differences between these members of the group with respect 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 external (as a rule). In all; the anterior edge of the superior oblique 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 Cebidae and Hapalidee we have an important difference. The choanoid slip is entirely absent; even in the Marmosets'I could 1 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 bv the sixth nerve; but its size and its attachment to the sclerotic vary much. |