156 DR. AVALTER KIDD ON THE [June 17, 



In the Horse a marked whorl, feathering, and crest are never 

 absent from the pectoral region ; a sj)ecimen that failed to show 

 this would be an abnormality, and the arrangement peculiar to 

 the horse is not only constantly present, but varies in width, 

 length, and definition, according to the muscular development of 

 the great masses of pectoral muscle, which ai'e so active in flexion 

 of the " elbow" of the animal. Indeed, it is roughly possible to 

 determine by this criterion in individual cases whether this or 

 that specimen and its immediate ancestors were high- stepping 

 animals or the reverse. 



The difference between the wide and long whorl, feathei-ing, 

 and ci-est on the pectoral region of a high- stepping, muscular 

 English cart-horse, and the narrow, ill-developed arrangement, 

 resembling that of a mule, on the coi-i'esj)onding part of a small, 

 ill-bred, shambling hackney, such as are very common in Italy, is 

 very striking in illustration of this point. 



In the Domestic Ass, with its small pectoral development and 

 shoi't step, the whoil, feathering, and crest are seldom present at 

 all, and most variable and rudimentary when they are present. 



In the Mule, with somewhat stronger muscle and higher action, 

 and yet in both respects far inferior to the Horse, the whorl, 

 feathering, and crest are more marked and more often present 

 than in the Ass. 



(3) The post-hu'nieral or axillary region occasionally furnishes 

 evidence of the locomotive activity of the animal and its ancestors ; 

 but the whorl, feathering, and crests found here ai'e never constant 

 in a large numbei' of specimens and even in horses are I'are, not 

 more than 2 per cent, of our domestic hoi-ses showing it. 



(4) In the inguinal hollow of many animals there are marked 

 traces of their personal and ancestral activity. In the Horse, the 

 well-known aj^iDearance of a graceful feathering, starting from a 

 whoil at the inguinal fold of skin and passing up to a marked 

 ridge at the level of the crest of the ilium, is as constant as the 

 corresponding phenomenon in the pectoiul area (text-fig. 31 , p. 1 57). 

 Here, again, a horse that did not present this featui'e would be an 

 abnormality. It varies, as any other chai-acter may, in degi-ee 

 and fulness of development, and is an evidence of a certain portion 

 of the anatomy and modern life-history of the species. The com- 

 parative anatomy of this arrangement has been elsewhei-e ^ moi-e 

 fully treated, and it is unnecessary now to allude to this, except 

 in the case of the Horse, Ass, and Mule. In the Horse it is 

 constant, well- developed, and the length of the feathering is never 

 less than half the distance between the margin of the inguinal 

 fold of skin and the crest of the ilium. In the Mule it is constant, 

 but never larger than this minimum development of the horse ; 

 and in the Ass seldom present, and, when present, it is but a 

 circular small whorl without any definite feathering or crest, and 

 is situated at the centre of the ilio-inguinal hollow. 



1 P. Z. S. 1900, p. 686. 



