1208 Mil. R. I. POCOCK ON THE EXTERNAL CHARACTERS 



the mistake of confusing the first with the fifth digits, for he 

 speaks of the double claw as being on the fourth, whereas it is 

 well known to be on the second digit *. This makes his descrip- 

 tion of the proportionate lengths of the digits (and the sizes of 

 their claws) different from mine. Of the pads he says : — " Three 

 elongate ill-defined pads at base of median digits, a larger and 

 better-defined tubercle behind base of hallux [= fifth digit]; 

 entire sole between hallucal tubercle and heel thickened and 

 pad-like.' 



The characters of the principal types of feet in the Sciuromorpha 

 may be tabulated as follows : — 



a. Fore foot with well-developed pollex, lobts of plantar pads 

 reduced to folds of flexible integument, ca-.pal pads very large, 

 no carpal vibrissas; hind feet with all the digits very long, 

 widely separable and united by webs up to tbe digital pads ; 

 lobes of plantar pad mostly obsolete, greater part of meta- 

 tarsal area covered by one large pad Castoridof. 



a'. Fore foot with pollex reduced to a mere excrescence or absent ; 

 lobes of plantar pads well developed, and as prominent as 

 carpal pads, carpal vibrissa always i^resent ; hind foot with 

 shorter digits, free from wel)s; plantar pad well developed; 

 metatarsus typically with two pads, a longer inner and a 

 smaller outer, both sometimes suppressed, 



h. A carpal rod supporting patagium, digits as in arboreal 



Scinridqs I'etauristidi.t. 



h'. No carpal rod. 



c. Fourth digit the longest, much longer than the 



second SciMric?;® (arboreal)., 



c'. Third digit the longest, fourth not much longer than 



second , Sdiiridce (terrestrial) . 



The Anus and External Genitalia. 



In the Sciuridfe and Petauristidse the anus and external 

 genitalia are normally separated. In the male the prepuce t is 

 prominent and situated some distance in advance of the anus, 

 being mostly long and pendulous and even retroverted, when at 

 rest, in the arboreal Squii'rels, the Bristly-Ground Squirrels, and 

 the Flying Squirrels, but shorter in the Marmots. Between it 

 and the anus there is in the Squirrels a very large scrotum in 

 the breeding season, but I have not been able to verify this in 

 the case of the Marmots. In the female the vulva is a semi- 

 circular or pointed process, situated a little below the anus, and 

 the clitoris is concealed within the labia. The anus has the two 

 normal glands in the Squirrels, Avhereas in the Marmots there is 

 an additional median gland. (Text-fig. 59, A, B, C.) 



The anus and external genitalia in Castoridte diff'er profoundly 

 from those of the Sciuridoe and Petauristidas. 



Externally the male and female are alike, owing to the 

 orifices of the alimentary canal and of the genito-minary organs 



* This error no doubt arose from the fashion now in vogue of twisting the hind 

 feet in made-up skins so that the hallux lies on the outer side of tbe foot so placed. 

 f The structure of the penis and bacuhim I must leave for another paper. 



