CHARACTERS OF SOME HYSTRICOMORPH RODENTS. 415 



groove extends downwards to the apex of the short, but pro- 

 jecting, haiiy prepuce, just above the tip of which posteriorly 

 may be seen the urinary orifice. (Text-fig. 28, D.) 



In a female Dolichotis there is a single small genito-urinary 

 orifice in the lower half of the naked subcaudal area, and there 

 is no external sign of clitoris or projecting preputial integument. 

 This is the normal condition presented by immature or unpaired 

 female Hystricomorphs. _ Possibly the vulva is closed by mem- 

 brane out of the breeding season. In the present instance 

 its orifice lay, no doubt, beneath the skin between the anus 

 above and the genito-urinary aperture mentioned above. (Text- 

 fig. 28, C.) ^ 



In (Javia po7^ceUus and aperea the vulva is near the centre of 

 the naked glandular anal area and separated from the anus by 

 the depression of the glandular sac. The very short prepuce 

 of the clitoris is situated some distance below the vulva. Before 

 pairing takes place, or out of the breeding season, the vulva 

 is covered with thin membrane, which easily ruptures when 

 stretched. (Text-fig. 28, B.) 



In the female Hydrochcerus, as stated below (p. 419), the vulva 

 is situated a short way beneath the anus, near the lower border 

 of the ano-genital area. It is a large, transversely extended, 

 dilatable orifice, containing and concealing a large, soft, fleshy, 

 linguiform clitoris on its ventral or anterior wall, and the orifice 

 of the urethra is some little distance away from the tip of this 

 clitoris. (Text-fig. 28, A.) 



In Ctenodaotylus the vulva is situated a little below the anus 

 aad the prepuce is elongated and perforated at the top (Text- 

 fig. 28, E.) (See also pp. 419-420.) 



a. Orifices of genital and nrinaiy oi-g-:ins visibl'e externalb' as 



separate apertures ; tlie prepuce and clitoris not involved in a 



sphincter embracing- also the anus. 



6. Urinary orifice visible beneath the vulva, not concealed 



vs'ithin a tubular prepuce. 



c. Orifice close beneath the vulva, remote from the tip of the 



, I'^llP'^ce • • • , , ■ • m,stvi.v, Mretldzon, Coendu. 



c . Untice not close beneath vulva, but nearer to the tip of 



tlie prepuce Atherura. 



b . Urinary onhce at apex of closed prepuce. Octodnn, Caprojnj/s, Basi/procta, 

 , „ .„ „ .^ , , . Ccelogem/s, Cavia, Kerodon, Cteuodacfi/lus. 

 a . Untices of genital and urinary organs involved in a common 

 integumeiital fold, so that externally there is a single large 

 urlno-getiital aperture, and this is involved in a sphincter 

 embracing the anus Hgdrocha^rus. 



According to Tullberg, Thrynomys by this table falls under I'. 



The Anus. 

 The anus in Hystrlx and Ath&rura opens in the middle of a 

 naked area, surrounded laterally and above by hairs and spines, 

 and inferiorly reaching to the genital orifice. There is a pair of 

 large, solid, anal glands opening by a slit-like orifice just within 

 the anal aperture, but below the termination of the rectum. The 



28* 



