OCR Text |
Show 1901.] SKULLS OF LEMURS AND MONKEYS. 141 within the fossa, and separate again almost immediately, so as to include between each other the thin bony plate above mentioned. In several of the younger specimens an intercalar bone is present as in Perodicticus. In specimen No. 67 d (Br. M.) it forms the medial continuation of the crista posterior, being limited anteriorly by the maxilla-with which it begins to co-ossify,- medially by the nasal, laterally by the planum, posteriorly by the frontal. In other slightly older specimens (Br. M . No. 67a, No. 67 c ; B. 0. S. No. 290) the intercalar bone is almost completely overgrown by the frontal. Text-fig. 43. Lacrymal region of Avahis laniger, about 4 nat. size. (Lettering as in text-fig. 26.) The malar terminates anteriorly above the interspace between m. 1 and the posterior premolar. Nycticebus. In this genus (see text-fig. 41) the crista posterior appears to be formed, either by the maxillary (laterally) and the frontal (medially)-joining in a suture in advance of, and above, the os planum,-or by two processes of the maxillary, joining in the same manner. Younger specimens show an intercalar bone which occupies the same position as in Perodicticus and Loris, and coalesces either with the maxillary or with the frontal. In some cases (N. javanicus, Br. M . No. 66 e; N. iardigradus, Br. M. No. 1550 b) a small process of the planum creeps upon the orbital margin between the maxilla and the frontal, or even advances into the fossa. There is no trace of the lacrymal within the orbit, nor, as has just been stated, on the orbital margin, where it seems to have been entirely covered by the maxilla, os planum, and frontal. Neither can the lacrymal be traced in the groove which in front of the crista posterior represents the fossa lacrymalis of other Lemurs. With the exceptions before mentioned, when the planum encroaches on the fos?a, the bottom of the latter is made up by two processes of the maxilla, which also encircles the canalis I. in front. The malar does not advance on the orbital margin farther than above the posterior end or the middle of the posterior premolar. In old specimens all the sutures are obliterated. |