No. 445-] 



HABITS IX MAMMAL. 



9 



lengthened and cylindrical as do the calcaneum and astragalus 

 in the frog. The hallux is large and opposable while digits II 

 and III are somewhat reduced, digit IV being the longest. In 

 Tarsius digits II and IV are clawed while the othn s hear flat- 

 tened nails. 



T/ie .V/(7///.— Cursorial adaptation has its cited upon the 

 skull only in the correlation that exists between long linil)s and 

 dolichocephaly, brought about by the necessity of reaclung the 

 ground on the part of a grazing animal. This is strikingly 

 illustrated in the horse series where the ineiease in the length 

 of the skull parallels the lengthening of the limbs. 



Saltatorial forms which, like Dipus, have lengthened the hind 

 limbs only, do not exhibit marked dolichocephaly, as the feeding 

 habits of the creature do not require it. The grazing kangaroos 

 however have a moderately elongate skull. 



T/w Vertebral Column. — Cursorial adaptation among mam- 

 mals is shown in the lengthening of the cervical vertebrje, espe- 

 cially in dolichocephalic forms, strikingly illustrated by the giraffe 

 and by Alticamelus of the Loup Fork of Colorado ^ a camel 

 showing the most remarkable convergence toward the giraffe, 

 although the latter is derived from a totally different stock. 



Among the saltatorial forms, especially those with brachy- 

 cephalic skulls, the tendency is toward the shortening of the 

 neck accompanied by a greater or less degree ot immobility. In 

 Pedetes cervicals 2 and 3 are so closely articulated as to elinn 

 nate motion, in Perodipus the a.xis and the next two vertebra- 

 are fused, while in Dipus all of the cervicals except the atlas 

 are coossified as in whales. 'I here is no increase or diminution 



dorso-Iumbar series seem to suffer little alteration in cursorial 

 form.s, though the lumbars increase in size in saltatorial tyjK-s. 

 The high number of vertebrae found in the horses is also found 

 in other perissodactyls and in the Proboscidea. and so is not to 

 be considered a modification coming within the scope of the 

 present discussion. In some saltatorial forms, as the jerboas, 

 an exceedingly short back is found ; but saltatorial adaptation 

 can exist without this feature. 



