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Show 144 DR. 0. I. FORSYTH MAJOR ON THE [Feb. 19, Ateles. In 14 out of 25 specimens examined, the fossa lacrymalis was completely encircled by the lacrymal (PI. XII. figs. 4 & 6), in six more cases the maxilla merely touched the fossa near its anteroinferior border. Only in five specimens was found a slightly more extended maxillary margin of the fossa, such as figured by Gegenbaur'. The supero-anterior angle of the lacrymal also protrudes more on the face than suggested by the mentioned figure. A lacrymo-nasal suture was found in 12 cases (PI. XII. figs. 4 & 6 ) ; a mixed condition, viz. a lacrymo-nasal suture on one side only, in three cases. Only in eight cases did I find a fronto-maxillary suture, which is always very limited, as described by Gegenbaur. It cannot be said that in every case the fossa lacrymalis is decidedly extra-orbital; this condition is rather an exception in Ateles, occurring when the crista posterior is more than usually prominent. Where the orbit presents no marked limits in this region, it is, as with Mycetes, a matter of mere individual appreciation whether we have to regard the fossa as lying inside or outside the orbit. That there are variations in this respect in Ateles, was already known to G. Fischer, who says that in a skull of A. paniscus the aperture of the lacrymal canal was situated " auf der Grenze der Augenhohle, oder auf seinem (sic!) Bande, aber doch immer mehr nach innen," whilst other skulls of the same species presented the same conformation as in the other species 2. Brachyteles. The skull of this rare monkey, of which I could examine only seven specimens-one in Leyden, six in the Natural History Museum-exhibits a very broad interorbital region, due in a great measure to the large development of the lacrymal. In spite of this, the anterior boundary of the fossa is for the greater part-in one case entirely-formed by the maxilla, which in two cases even protrudes into the fossa. In the upper region the lacrymal advances on the face, so that the fronto-maxillary suture is either very limited, or in two cases-B. hi/poxanthus, Levden; B. arachnoides, Br. M . No. 43.10.12.2 (PI.* XII. fig. 1 ) -a "lacrymo-nasal suture is present. Callithrix. Sixteen skulls examined.-The anterior margin of the lacrymal fossa is always bordered by the maxilla, at least on its lower half (PI. XII. fig. 7), and sometimes (0. donacophila) on its whole extension. The antero-superior angle of the lacrymal protrudes forwards, least of all in C. donacophila, which therefore exhibits a very broad fronto-maxillary suture; in all the other species there is 1 Op. cit. p. 175, fig. IIB. 2 G-. Fiscber, Anatomie der Maki, p. 90 (1804). |
