Contributions from the E.M. Museum of Geology and Archaeology of Princeton College. Bulletin no. 3.

  • College of New Jersey (Princeton, N.J.). E.M. Museum of Geology and Archaeology.
Date:
1883
Catalogue details

Licence: Public Domain Mark

Credit: Contributions from the E.M. Museum of Geology and Archaeology of Princeton College. Bulletin no. 3. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    cesses of the squamosal. In the Lophiodonts and Tapirs these processes are widely separated, leaving the auditory meatus open below; a state of things which we also find in the Eocene Amynodontid(E. In Acerathcrium the two processes approach each other, and in one of our specimens from Dakota are almost in contact. In Aphelops they touch each other, and in Rhinoce- rus they are co-ossified. Ceratorhinus and Atelodus, which are persistent Miocene genera, have the meatus still open. Hyraco- don agrees with the other Miocene types in having these pro- cesses widely separated. Other progressive modifications, as the change of the occipital condyles from projecting to sessile, the conversion of the broad and transversely directed post-glenoid process into a styliform shape, the appearance and increase of the post-cotyloid process, the thickening of the posterior edge of the ascending mandibu- lar ramus, might be followed out in the same way, each one gradually leading up to the modern forms, in all of which re- spects Orthocynodon represents the first stage. The Brain likewise indicates a continual advance, at least in size. In Hyrachyus there was quite a large brain for an Eocene mammal. The hemispheres were well developed and rounded, though little convoluted (as far as can be judged from a cranial cast); the olfactory lobes were large, and the cerebellum was lodged in a very distinct fossa. Of the details of the brain in Orthocynodon we know nothing, but judging from the general shape of the cranium, it appears to have been somewhat longer and narrower than in the Lophiodonts. Compared with the Eocene Rhinoceroses, Accratheriuin had a much higher type of ‘ brain. The hemispheres are much larger, both in proportion to i the skull and to the cerebellum ; they are well convoluted, broad, rounded and somewhat depressed, and seem to have slightly overlapped the cerebellum. The olfactory lobes are consider- ably reduced in size. This brain is not unlike that of the mod- . ern species. j Dentition. In the dentition the steps of progressive modi- \ fication are very clearly seen. In Orthocynodoji the only change from the Lophiodonts, besides the transformation of the molar teeth, is the enlargement of the lower canines and perhaps the I loss of one pair of lower incisors. In Amynodon the canines are .] procumbent and compressed, and, “ taken in connection with the rest of the anterior dentition, they prove conclusively that the ^ large lower teeth, usually regarded as incisors in Acerathcrium and many other members of the Rhinoceros family, are really a canines” (Marsh’). This view of the homologies of these teeth >2 is completely confirmed by their position in the Bridger genus, which is like that of all the Eocene Tapiroids. Their compressed