OF THE BEAVER AND OF SOME SQUIRRELS. 1207 



comb, and the claws of the first and second are sharper and more 

 curved than those of the others. The greater part of the lower 

 side of the digits and of the webs is naked, but the proximal ends 

 of the digits and of the webs is thickly granular like the rest of 

 the sole back to the heel. The greater part of the metatarsal 

 area is covered with a big pad extending on the outer side almost 

 as far as the base of the fifth digit, and on tlie inner side about 

 halfway between the heel and the hallux, where its edge turns 

 obliquely across the sole to meet the outer edge in a widely- 

 rounded curve. This pad is widest across its middle, gradually 

 and slightly narrowed behind and greatly narrowed in front. 

 Between it and the base of the hallux, and separated from it by 

 a narroAver or wider furrow, lies a second much smaller pad, the 

 outer edge of which forms the margin of the metatarsal area in 

 front of the inner portion of the larger pad. The distal third of 

 the smaller pad is at the base of the hallux. In front of these 

 pads the skin is folded and gi-ooved, but shows no definite trace 

 of plantar pads. It is difiicult to homologize the two pads above 

 described Avith the pads on the sole of the hind foot in the 

 Sciurida3. Tentatively I adopt the hypothesis that the smaller 

 inner pad represents the inner or hallucal element of the plantar 

 pad, which is often large in the Sciurida?, and that the larger pad 

 represents the two normal metatarsal pads fused together and 

 blended with the rest of the integument. The disappearance of 

 the main elements of the plantar pads in Castor is in keeping 

 with their partial or complete suppression in other fully Aveb- 

 footed aquatic forms like the Ooypu and some others ; and the 

 retention of the pa,ds on the metatarsus is to be explained by 

 the beaver's habit of walking on its heels when carrying objects 

 on land. Whether the above suggested explanation be true or 

 not, it is evident that in the structure of its fore and hind 

 feet the Beaver diflers greatly from the Squirrels. (Text- 

 fig. 58, B, 0.) 



My description of the feet was taken from the European 

 species, Castor fiber. The American species has similar 

 feet. 



Miller's description of the feet of the European species differs 

 materially from mine. The fore foot, according to him, has five 

 palmar tubercles, " the three at bases of median digits large, 

 ill-defined, that at base of thumb not so large as the others but 

 better defined, its outer surface tending to become smooth and 

 horny, the posterior pad largest, covering about one-third of 

 entire palmar surface." It seems clear from this that the inner 

 of the three above-mentioned tubercles at the base of the poUex 

 is the horny gi^ooved pad I identify as the inner carpal pad. If 

 Miller's interpretation is correct, this is the poUical or inner 

 element of the plantar pad. His " posterior pad" must be the 

 large pad I describe as the outer carpal pad. 



In his description of the hind foot it is evident Miller has made 



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