CLASSIFICATION OF THE SCirRIDJ<:. 217 



The baculum of an example of liatufa gigantea from Gokteik, 

 IST. Shan States, in the Britisli Museum, is simple and shaped in a 

 general way like that of Fanmnhulus palmarum, but is relatively 

 much shorter and stouter. It is expanded at the base, and in 

 lateral view its upper and lower edges are respectively concave 

 and convex, but with a sinuous outline. The distal end of the 

 lower surface is irregularly bevelled up to the apex, which is 

 narrowed but not pointed, and there are four subsymmetrically 

 arranged rows of small irregularly spaced bony spicules on this 

 distal portion, which from the dorsal or ventral aspect is seen to be 

 slightly asymmetrical. It measures 10 mm. (Text-fig. 20, E, F.) 



The baculum of a specimen, referred to the same species, from 

 Darjiling is very similar, but more strongly bevelled and upcurved 

 distally, the apex being a little expanded; and one of R.fellii 

 from Yin, L. Chindwin, is also very like it. But a baculum of 

 a captive specimen * of R. indica, without locality, also in the 

 British Museum, is very different. It is a much larger and 

 longer bone, about twice the length of the others if straightened, 

 and has its distal half bent strongly upwards at an obtuse angle, 

 a shoulder-like excrescence on each side marking the bend. This 

 distal upturned portion is quite symmetrical, expanded basally 

 and apically, concave laterally, hollowed inferiorly, and tridentate 

 at the tip, the median tooth being a little longer a,nd set further 

 back than the laterals. This baculum, measuring in a sti-aight 

 line from base to apex 14 mm., may be perfectly normal. Its 

 strongly upturned distal portion evidently corresponds to the 

 slightly upturned denticulated, bevelled distal portion of the 

 other bacula of the genus. (Text-fig. 20 G, H.) 



Setting aside Rheithrosciuras macrotis, above referred to as 

 probably having a baculum shaped like that of Sciuribs vulgaris, 

 the rest of the Oriental genera of Sciuridse, as Tliomas showed, 

 have bacula specialised by the development, on the upper side, of a 

 blade which is hinged to the shaft in such a way as to be slightly 

 movable from right to left. The blade projects backwards, and a 

 longer or shorter portion of its posterior end is free from the 

 shaft. Bacula of this kind belong to two main categoi'ies — one, 

 characteristic of Calloscmms, the other of Tomeiofes. But distinct 

 as the bacula of these two kinds are in their extreme forms, 

 there are indications of intergradation between them f. 



In Callosciurus prevosii, the type of Callosciurus, the glans is 



* Bacula of mammals kept in confinement are sometimes abnormal. 



f In his preliminary description of these bacnla Thomas wrote : — " In position in 

 the penis the blade points to the right, its edge cutting outwards." Again, the baculum 

 of Callosciurus is said to have " a narrow blade set on the side of it, in the con- 

 cavity of its general curvature .... the greatest breadth [of the blade] is only about 

 one-fourth to one-sixth of its length." This, however, does not agree with my 

 observations, for I find in all the fresh or spirit-preserved material examined that the 

 concavity of th.e shaft of the baculum and the blade are on the dorsal or upper side of 

 the bone. If the lilade were on the right side, the asymmetry of the baculum vrould 

 be extreme and the edge of the blade would cut the right side of the vulva. I have 

 no doubt that the function of the blade is to make a vertical cut of the integument 

 (hymen) covering the orifice of the vagina. 



