TRANSACTIONS OF THE AMERICAN PHILOSOPHICAL SOCIETYsomewhat larger. Here also the ossified membranes around the mouth have become enlarged and folded back over the hyoid arch, while the bony membrane on the latter has likewise become enlarged and folded over laterally to the remaining gill-arches. In the ostracoderms there is no evidence that either the mouth or the minute gill-openings were supported hy jointed arches like those of sharks. But, as already noted, there was a continuous supporting tissue in the septa between the gill chambers.It is hardly necessary to review in detail the evidence for the now commonly accepted conclusion that the primary jaws, or oromandibular arches of the gnathostome vertebrates are serially homologous with the branchial arches. (See Goodrich, 1930, pp. 396-^23.) Even in the adult shark (Fig. 4) the topographic correspondences of the jaws themselves to the branchial arches and of the adductor mandibulae muscles and their nerves to the flexor muscles of the branchial arches and their nerves, reinforce the embryological evidence as recently set forth by Sewertzoff (1927). Sewertzoff (1927, Taf. 29, fig. 10) has shown that in the embryo shark the labial cartilages which lie on either side of the oropharynx also have vestigial pouches suggesting those of the gill-arches. These pre-oral cartilages reach a high degree of functional elaboration in the chimaeroids, where they somewhat suggest small jaws lateral to the main jaws (Sewertzoff, 1927, Taf. 31). According to Sewertzoff, the mandibular arch of gnathostomes represents the third of the series; this, together with the hyoid arch and five to seven normal gill-arches of sharks, would make nine to eleven in all. The view of Ayers (1921) that the jaws of gnathostomes have arisen from rod-like structures in the velum of Amphioxus does not appear very tenable in the light of more direct evidence for the view summarized above. The palaeontological evidence, illustrated especially in the acanthodian and cladoselachian sharks (Fig. 5), reinforces the embryological and morphological evidence in favor of the strict serial homology of the oromandibular arch with the hyoid and branchial arches.Very obscure and complex is the problem of the serial homologies of the dorsal segments of the mandibular, hyoid and branchial arches. AUis (1915, 1923^, 1925^) has maintained that the trabeculse of the embryonic chondrocranium represent "premandibular arches which have swung upward to fuse with the membranous brain case," a view originally proposed by Huxley (Goodrich, 1930, p. 238). Also that the polar cartilages which connect the trabeculae with the parachordals represent the dorsal elements (pharyngomandibulars) of the mandibular ardhes, of which the palatoquadrates represent the epimandibulars while the Meckel's cartilages represent ceratomandibulars. But both Sewertzoff (1928, p. 202) and Goodrich (1930, p. 238) agree that the trabecular and polar cartilages are part of the axial skeleton or neurocranium. The Hyomandibular ProblemAs to the h...
Important skeletal remains of Eocene Primates of the genus Notharctus Leidy, including skulls, teeth, and incomplete skeletons, were obtained in Middle Eocene strata of the Bridger Basin, Wyoming, by American Museum expeditions under Mr. Walter Granger in 1903 and 1904. This delicate material was freed from the matrix and prepared for study and exhibition chiefly by Mr. Albert Thomson. It was generously assigned by Professor Osborn and Dr. Matthew to the writer to be described and compared with the earlier collections of Eocene Primates in this Museum. These collections have already been studied and described, as to their diagnostic generic and specific characters, in several papers in the Bulletin of this Museum by Osborn (1902), Matthew (1915), and Granger and Gregory (1917), so that the following pages deal chiefly with the morphology and evolution of the genus Notharctus and with the relationships of the Notharctinse with other groups of primates. Preliminary reports on this subject were made by the present writer in 1913, 1915, and 1916 in the papers cited in the bibliography. The auditory region and ossicles of Notharctus oshorni were very skilfully freed from the matrix by Mr. Abram E. Anderson, who also prepared many other specimens and all the photographic illustrations for this work. The line drawings, unless otherwise noted, were drawn under the writer's direction by Mrs. Ehzabeth M. Fulda. A few words of explanation may be offered as to the illustrations which are reproduced from the works of other investigators. If, according to a conventional method, one had given drawings or photographs only of the Notharctus material itself, that would have been a sufficient record for the few investigators who, in the course of future decades, would read the text with care and make their own detailed comparisons after having duly assembled the literature of the subject and with their own specimens for comparison in hand. But if (as the important nature of the material seems to warrant) it is desirable to make the whole subject available also to a wider circle of scientistsspecialists in other fields who have neither the inclination nor the facilities for a first hand study of this material,then it is necessary to supply abundant comparative illustrations in order to show at a glance what are the resemblances and differences between these Eocene Primates and other members of the same order. Accordingly the writer has reproduced for comparison many of the excellent figures of the Eocene Primates of Europe published by Dr. Stehlin in his Critical Catalogue of the Swiss Eocene mammals, and a few of the remarkable engravings of the osteology and myology of recent indrisine lemurs in the memoir by Alilne Edwards on the Anatomy of the Lemurs of Madagascar. Cuvier's and Laurillard's "Planches de Myologie" have yielded se^"eral useful illustrations, and the same is true of other sources which are acknowledged in tlie legends of the text figures. Some of the photographs of primate skulls which were made by Mr. Anderson for...
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