1902.] HAIR-SLOPE IN MAMMALS. 149 



whorl, feathering, and crest of the pectoral region of a Horse with 

 what is found in the closely-allied Ass and Mule. In the Horse 

 it is large, symmeti'ical, never absent, especially mai-ked in high- 

 stepping horses, whether cart-horses, or horses selected because of 

 their high action in trotting. Its size, indeed, is a measure of the 

 activity of the pectoral muscles and flexors of the fore-limb. In 

 the Ass it is either absent (and this is the rule) or, when present, 

 it is rudimentary ; in the Mule it is more frequently present than 

 in the Ass but still ixidimentary. These degrees of development of 

 the pectoral whorl, feathering, and ci'est in Horse, Ass, and Mule 

 correspond closely with the locomotive habits of the three 

 animals. 



In the six Prejevalsky's Wild Horses in the Society's Gardens 

 it is also absent, as one would expect in a wild animal. In 

 Zebras and Eqitus asinus, though so closely allied in foi-m to 

 the Horse, but so luilike in their wild and independently locomotive 

 life, it is absent. 



(2) On the Fore-limb the two types of arrangement of hair have 

 been fully described ^ elsewhere, and it is only necessaiy to point 

 out here their relation to the two main recumbent attitudes, those 

 of the Carnivore and the Ungulate ; the exceptions found among 

 the latter have been given elsewhere ^. 



(3) Abdomen. — The ventral surface of the thorax and abdomen 

 show little interference with the normal slope of the animal's hair 

 caused by its attitudes in lying. It is perhaps not unnecessary 

 to point out this fact, because in such a study negative facts may 

 weigh considerably in support of a positive contention if explana- 

 tions in accordance with these be foi-thcoming. When lying on 

 the ventral sui-face of its abdomen, an animal rests very little on 

 the thorax because of the support of the fore- limbs ; and in this 

 position any tendency to slide forwards which may exist serves 

 but to confirm the normal slope of hair from cephalic to caudal 

 extremity, and thus the absence of any marks on the ventral 

 surface, due to the recumbent position, is fully accounted for. 



On the lateral aspect of the abdomen there is found in nearly 

 all Carnivoi'es and Ungvila,tes an area of reversed hair, where the 

 " knee " of the animal rests in flexion, during lying and sitting, 

 against the flank. The extent of this area is vaiiable and is 

 usually mai'ked off by a margin, showing where the general 

 backward and downwai'd direction of haii- on the flank is inter- 

 rupted by the pressure of the flexed hind-limbs. In many animals, 

 there is a genei'al forward slope of the hair on the hypogastric 

 region till it reaches a point on the abdomen where apjDarently 

 the effect of the pressure of the hind-limbs ceases, and at this 

 point a tuft is often seen, especially in horses. It is shaped very 

 much like a small stack of corn, and stands out from the rest of 

 the surrounding hair. I have seen a definite ridge with two tufts 

 at the meeting-place of the stream of hair from the thorax and 



1 ' Use-Inheritance,' A. & C. Black, 1901, pp. 28, 29. 



2 Proc. Zool. Soc. 1900, p. 686. 



