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Show 236 MR. F. E. BEDDARD ON [Apr. 7, 5. Notes on the Anatomy of Dolichotis patagonica. By FRANK E. BEDDARD, M.A., Prosector to the Society. [Received April 7, 1891.] I am not acquainted with any paper dealing with the structure of this Rodent; the following notes may therefore be of some use. Alimentary Canal and Viscera. The hard palate, as in many Rodents, is narrow anteriorly, and the ridges are in consequence much reduced and modified. The accompanying drawing (fig. 1, p. 237) shows that they are only represented by two pad-like structures (a), each of which terminates in a pair of horny processes directed backwards; those of the posterior ridge are the longest. As the palatal ridges are characteristic in various Rodents, I have thought it worth while to illustrate their very peculiar form in Dolichotis. There are no ridges at all between the molar teeth ; the mucous membrane is there perfectly smooth. The tongue is divisible into two regions-a broadly oval tract behind and a narrow long anterior portion; the former has two circumvallate papillse, and a large " Mayer's organ " on each side measuring about half an inch in length. The intestines measure altogether 18 feet 6 inches. The ccccum is large ; it measures along the greater curvature, from the free extremity to the exit of the colon, about 18 inches; these measurements apply to the gut when distended with alcohol. Its structure appears to be a little similar to that of the Capybara as described by Garrod 1; both the ileum and colon open into a pouch separated by an incomplete valve from the rest of the csecum ; their apertures are not very close together, about an inch apart; the aperture of the colon is guarded by a sphincter. One lip of the ileo-csecal orifice is formed by the fold which divides the csecum proper from the colic pouch. From the sphincter valve of the colon three ridges like the typhlosole of the earthworm's intestine pass along its inner surface ; these are in addition to the numerous closely-set fine ridges which traverse the first part of the colon running parallel to each other ; these latter are very evident in the csecum of the Paca, of which I have a dried specimen. The first of these ridges can only be followed for a short way; the other two, on the contrary, extend for a very long way down. I 1 " On the Csecum coli of the Capybara (Hydrochceruscapybara)" P. Z. S. 1876, p. 19. Garrod, however, states in that paper that " neither in Cavia, Bolichotis, Capromys, nor in any of the allied forms with which I a m acquainted, does the strong sigmoid curve of the large intestine, at the commencement of the sacculated caecum, develop into a true secondary caecum in the manner that it does in the Capybara." The difference appears to be chiefly in the fact that the colon in Capybara is prolonged beyond its opening, thus forming the second caecum ; the arrangement in Bolichotis is more like that of Ereihison as figured and described by Mivart. I may mention that in Sphingurus prchensilis there is no such separation of the csecum into two chambers. |
