Studies of Eocene Mammalia in the Marsh Collection, Peabody Museum. Pt. II. Primates / by J. L. Wortman.

  • Wortman, J. L. (Jacob Lawson), 1856-1926.
Date:
[1903-1904]
Catalogue details

Licence: In copyright

Credit: Studies of Eocene Mammalia in the Marsh Collection, Peabody Museum. Pt. II. Primates / by J. L. Wortman. 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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    character par excellence in which they have made the greatest progress and in which their evolution lias been most marked. The very early development of prehensile hands and feet and the better arrangement of the cerebral circulation have been intimately associated with this progress and are therefore factors of prime taxonomic value and importance. In other words, the Primates have adapted themselves more widely to environment than any other mammalian group, in consequence of which they present well-defined skeletal indices or equiva- lents, so that whenever they are sufficiently preserved, it is possible to recognize them with a degree of certainty not usuall}T found in other groups of the Mammalia. Characters of the Cerebral Circulation. As regards the first set of these characters (the enlargement of the brain), like all other specialized features which come to distinguish a group or order in the final or advanced stages of its evolution, they are of necessity less distinctly marked in the earlier representatives than in the later ones ; so that, as we approach the point of origin, greater and greater difficulties are experienced in the application of such characters as a real test of affinity. Thus it is that we find in the less specialized members of the Primates, such as the lemurs and the oldest true monkeys, the relative development of the cerebral hemi- spheres to be little, if any, greater than that of many of the Insectivora; and were we compelled to depend upon this char- acter alone, it would be in many instances practically impos- sible to determine whether the animal in question were a Primate or an Insectivore. Fully recognizing the importance of thus clearly distinguish- ing between these small-brained Primates and other contiguous groups, in the matter of certain cranial characters, I have been led to make a careful and somewhat exhaustive study of the manner in which the blood supply is furnished to the cerebral hemispheres. Especial attention to this subject has been given, on the assumption that it must have been not only intimately associated with the progressive enlargement of the cerebral hemispheres in the Primates, but was in a way not now clearly understood, in some degree at least, responsible for it. If it is true that certain fundamental differences of this character exist between the several orders, the practical advantage to the pale- ontologist will be great, since it is only on very rare occasions that he has to deal with complete skeletons of the extinct species. In order to bring out.these characters more clearly, I shall first consider the Insectivora, and I begin by quoting Hux- ley’s statement of the course of the entocarotid in the hedge-