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Show 456 M R. F. E. BEDDARD ON HAPALEMUR GRISEUS. [Julie 16, W e must undoubtedly regard this bloodless fold of membrane- the frenum-as Mr. Treves1 has pointed out, as being the true mesentery of the csecum, and the development of the lateral folds as an entirely secondary process. Looking at the matter from this point of view Hapalemur is evidently, when compared with Lemur, a specialized type. It is not, however, so easy to decide whether the Lorisinse or the Lemurinse include the older types. Perhaps the presence of two lateral folds in the Lorisinse is evidence of a more specialized condition than is shown by either the Lemurinse or Galagininse, where only one is developed. On the other hand, the independence of the frenum and the lateral fold in Loris and the Potto, as contrasted with their fusion in Lemur (also, however, in Nycticebus), might be used as an argument on the other side. There can, however, be no doubt, and that is rather the point upon which I wish to dwell in the present communication, that Hapalemur is so far a specialized type of Lemur in that it has lost the true mesentery of the csecum. Whether this is, or is not, correlated with the altered form of the cascum itself is not a matter of importance, since in any case the organ itself shows a departure from the ordinary Lemurine csecum in its shape. Brain. The brain was carefully extracted, and is in an excellent state of preservation. In the hardened brain I have made the following measurements, which are placed side by side with corresponding measurements of well-preserved brains of Lemur anjuanensis and Galago crassicaudatus. Total length Greatest bread t h Length of hemisphere Greatest depth Hapalemur. nun. 36 26-5 33 19 Lemur. mm. 42 33 37"5 23-5 Galago. mm. 35 27 32 17 From these measurements it follows that the brain of Lemur is broader as well as deeper than that of Hapalemur, that the brain of Galago is broader but shallower than that of Hapalemur, and that the brain of Lemur is just perceptibly broader but considerably deeper than that of Galago. The narrowness of the brain of Hapalemur, as contrasted with the other types used for comparison, is indeed apparent to the eye without making accurate measurements to prove it. As will be also seen from the above table, the difference in length between the brains of Hapalemur and Galago is very small; the 1 "The Anatomy of the Intestinal Canal and Peritoneum in Man." Hun-terian Lecture, 1885. London, 1885. |