OCR Text |
Show 1901.] SKULLS OF LEMURS AND MONKEYS. 133 fossa is not yet situated within the orbit." In Ateles the lacrymal forms the greater part of the border of the fossa-including the upper half of the crista anterior and its antero-superior angle-and projects towards the nasal, so that there is only a narrow suture between the frontal and the frontal process of the maxillary. In Mycetes the lacrymal projects farther still, uniting with the nasal; besides, the whole of the fossa is encircled by the very large lacrymal, "a position which most approaches to that of Lemurs." In Nyctipithecus (N. trivirgatus), the third platyrhine genus mentioned, the whole of the crista anterior is formed by the maxilla, thus presenting a condition more closely approaching the Simiidae and M a n than even in the Cercopithecidae. Nyctipithecus recalls Mycetes and Ateles only in the projecting of the antero-superior lacrymal portion, which separates almost completely the maxillary from the frontal. In the Cercopithecidae (" Semnopithecus, Inuus, Cercopithecus, Cercocebus, Cynocephalus "), although the position of the lacrymal fossa is undoubtedly orbital, it is almost entirely encircled by the lacrymal bone, the crista anterior being either entirely formed by the latter bone, or by the lacrymal together with the frontal process of the maxillary. All the Cercopithecidae exhibit an enlargement of that part of the lacrymal (the hamulus of Human anatomy) which borders the fossa laterally, so that we find here an extensive plane. Various individual variations are mentioned, to which will be referred further on. Gegenbaur sums up in the following words:-" Das von Befunden an Thieren Angefiihrte geniigt, um zu zeigen, dass dem Lacrymale in niederen Zustiinden eine faciale Ausdehnung zukommt, und dass die Pars facialis in den hoheren Abtheilungen Kiickbildungen erleidet, wodurch die Pars orbitalis zur ausschliesslichen Reprasentanz gelangt. In dem Maasse als diese Kiickbildung stattfindet und dadurch die vordere Umgrenzung des Canalis lacrymalis vom Thranenbejn aufgegeben wird, tritt der Stirnfortsatz des Ober-kiefers dafiir ein, und gelangt vorn zur Umschliessung jener Grrube. Das ist beim Menschen wie bei anthropoiden Affen zur Hegel gewordeu : der Hamulus ist der Rest der Verbindungs-strecke von Pars orbitalis und P. facialis . . ." '. It is necessary to insist upon two results of this investigation : (1) the curious circumstance that, whilst of the three platyrhine genera mentioned, two represent the lowest stage in Monkeys, the third one on the contrary represents the highest, if we except the Simiidge. And (2) that the encircling of the whole of the lacrymal fossa by the largely developed facial portiou of the lacrymal-occurring in the Lemurs and in Mycetes-is considered to be the lowest condition, from which the condition in higher forms is said to be derived by a gradual reduction of the pars facialis, the reduction being initiated by the maxillary replacing the lacrymal in front of the fossa. 1 Op. cit. p. 176. |