14 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 122 



present, including modifications in the musculature and vertebral 

 column, reduction in the number of hind toes, lengthening of the 

 hind feet, shortening of the forelimbs, fusion of the cervical vertebrae, 

 and modifications of the tail. To be sure, most rodents possess the 

 ability to stand on their hind legs and walk or even hop for a short 

 distance, but sustained bipedal saltation does not occiu* as a normal 

 behavior pattern with the absence of certain morphological and 

 physiological correlates. In the group under study, full bipedal 

 locomotion was exhibited only by ]\Iicrodipodops, Dipodomys, Allac- 

 taga, and Jaculus. The latter two genera are more advanced in that 

 the fii'st and fifth toes are reduced (Allactaga) or absent {Jaculus) and 

 in both forms the metatarsals are fused to form a "cannon bone." 



Comfort movements.^ — -Sandbathing: Sandbathing is a complex 

 movement pattern functional in dressing the pelage. It is composed 

 of several distinct behavioral units, including side rubbing, ventrum 

 rubbing, writhing from side to side, and rolling on the back. All 

 these units are part of the total behavioral inventory of most rodents 

 and other mammals; however, the organization of these units into a 

 specific pelage-dressing pattern tends to be taxon-specific (Eisenberg, 

 1963c). The species-typical movement complex termed "sandbath- 

 ing" is a normal part of the behavioral repertoire in most rodents 

 that have adapted to arid habitats. It should be understood that 

 sandbathing is not confined to desert rodents alone, but that the 

 frequency of occiu'rence and stimuli necessary to ehcit the pattern 

 are characteristic of desert-adapted species. In the ciu^rent study, 

 Gerhillus gerbillus, G. nanus, Tatera indica, Meriones unguiculatus, 

 M. hurrianae, Pachyuromys duprassi, Allactaga elator, Jaculus jaculus, 

 J. orientalis, Peromyscus crinitus, and all species of Microdipodops, 

 Perognathus, and Dipodomys exhibited functional sandbathing. 

 Dressing the pelage by rolHng or rubbing in dry soil may be accom- 

 plished potentially by any of the several discrete movements men- 

 tioned above. Typically the animals exhibit digging movements 

 with the forepaws and the kicking back of accumulated earth with 

 the hind limbs. Digging movements serve to dust the fiu* of the 

 ventrum and often, while digging, the anunal may exhibit slight 

 forward extensions of the body as it presses its ventrum against the 

 substrate. The components following digging and kick back are 

 classified as a side rub, ventral rub, or rolling over, but this tripartite 

 classification masks some subtle details. Since the side rub and 

 ventral rub commonly occurred in the series of rodents studied, I 

 include a brief description of the variations: 



The side rub : This may involve lowering the head to the sub- 

 strate and sliding forward on the side while first extending and then 

 flexing the torso. The action may be swift with only a slight exten- 



