OCR Text |
Show 310 DR. A. KEITH ON THE CHIMPANZEES. [Mar. 7, the long nasal bones of the loAA'er Catarrhini; in all the other Anthropoids and in Man they have undergone marked retrogression, especially in the Orang. The nasal bones, as can be seen in the living Chimpanzee, extend doAvnwards to the level of the lower border of the orbit and are nevTer 0A*er 25 m m . long ; in the Gorilla they extend much lower down and are never less than 40 m m . in length. The nasal bones of the Gorilla SIIOAV a sharp median ridge, evident in the living animal. This ridge appears at adolescence and sometimes disappears in very old animals. A trace of this ridge is seen on the nasal bones of the Central-African Chimpanzee. The nasal bones unite before birth in the Gorilla, at or after birth in the Chimpanzee. At their upper end the nasal bones of the Gorilla always project Avithin the interfrontal suture, sometimes to a slight degree, frequently to a very considerable extent, and at their lower ends unite into a spine in over 60 per cent, of skulls. On the other hand, the nasal bones of the Chimpanzee seldom project within the interfrontal suture and only to a slight extent, the examples occurring mostly in Central-African Chimpanzees, and SIIOAV an inferior spine in only 15 per cent, of skulls, and these Avere mostly from Central Africa. The inter-orbital breadth and the shape of the bridge of the nose have frequently been used as characters of differentiation. They both depend on age, and to some extent on sex. All through the life of a Chimpanzee the bridge of the nose keeps changing in conformation, owing to the continual growth of the lachrymo-ethmoidal air-sinus : the convex bridge of the young adult becomes converted into the flat or depressed bridge of the old adult. The interorbital breadth is practically the same for Gorillas and Chimpanzees, being greater in males than females, but the bridge of the nose in the Gorilla never becomes flattened and depressed like that of the Chimpanzee. In her AA'ide, smooth, rounded alar nasal folds, Johanna, and all the Chimpanzees ascribed to the variety of Avhich she is an example, shows a marked Gorilline feature. A. niger never possesses these folds so markedly, although they do increase in size with age ; but in the Gorilla they extend almost to the margin of the lip, the middle part of Avhich shows a widely grooved philtrum. In Johanna a distinct trans\rerse groove marks the upper lip from the nose, and such a groove occurs always in Chimpanzees. The middle and inferior turbinate bones of the Chimpanzee are more convoluted than in the Gorilla, and the nasal duct less inflated. In development, the palatine processes of the palate-bone of the Gorilla frequently fail to meet, giving rise to a form of cleft palate; they always, Avhen they unite, leaA'e an open angle between them: the corresponding processes in the Chimpanzee are always well developed and unite so as to leave the bony palate with a transverse posterior border. The nasal spines of the premaxilla are commonly present in the Gorilla (17 out of 28) and seldom in the Chimpanzee (5 out of 43). The nostrils are widest in the Gorilla. The anterior opening of the nasal cavity in the adult Chimpanzee |