236 MR. F. E. BKDDARO ON [Apr. 7, 



5. Notes on the Anatomj of DoUcJwtis pataffonica. By 

 Frank E. Beddard, M.A.^ Prosector to the Society. 



[Eeceived April 7, 1891.] 



I am not acquainterl with any paper deaUng with the structure of 

 this Rodent ; the following notes may therefore be of some use. 



Alimentary Canal and Viscera. 



The Tiard 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, 1 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 papillae, 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 ccBcnm 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 he a little similar to that of the Capybara 

 as described by Garrod ' ; both the ileum and colon open into a 

 pouch separated by an incomplete valve from the rest of the caecum ; 

 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-caecal orifice is formed by the fold which divides the caecum 

 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 

 caecum 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 



^ " On the Caecum coli of the Capjbara {Hydrochcerus capybara) " P. Z. S. 1876, 

 p. 19. Garrod, however, states in that paper that " reither in Cavia, Dolichotis, 

 Capromys, nor in any of the allied forms with which I am acquainted, does the 

 strong sipmoidcurve of the large intestine, at the commencement of the sacculated 

 ciBcum, develop into a true secondary crecum 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 cteciim ; the 

 arrangement in DoUcfiotis is more like that of Ere/hic-on as figured and 

 described by Mivart. I may mention that in S2}hingurus prcheiisilis there is 

 no such separation of the caecum into two chambers. 



