24 



THE HORSE 



in walking. The scapula or shoulder-blade has a very 

 oval form, resembling that of a carnivore more than that 

 of any existing ungulate. The clavicles or collar-bones, 

 as previously mentioned, are lost. 1 



The humerus, or upper-arm bone, presents a charac- 

 ter not found in any of the existing ungulates, although 

 common in the carnivora — that of a perforation, or fora- 

 men above the inner condyle. The two bones of the 

 forearm, are, as in all generalised forms, both fully 

 developed, the ulna being of large size throughout its 

 length. 



The structure of the wrist, or carpus, is of great inte- 



1 In using this expression the assumption is made that Phena- 

 codus, and, in fact, all other mammals, are derived from forms having 

 clavicles, and that the absence of these bones is a case of specialisa- 

 tion, an assumption supported by the facts that the presence of 

 clavicles is the rule in birds, reptiles, and amphibia ; that they are 

 well developed in various orders of mammals not otherwise closely 

 associated, as marsupials, edentates, insectivores, and primates ; and 

 that they are also found, though often in a more or less vestigial 

 condition, in rodents and carnivores. These facts all tend to show, 

 if they do not conclusively prove, that the presence of the clavicle 

 is the typical condition, notwithstanding its complete absence in 

 extensive groups of mammals, as the ungulates and cetacea. 



Since the above was in type the discovery has been announced of 

 the presence of a rudimentary and transient clavicle in an early embryo 

 of a sheep. This affords a complete confirmation of the view above 

 expressed, and is a most astonishing instance of the persistence of 

 a structure in the embryonic condition, which has, as far as our evi- 

 dence tells, been absent in the adults during the whole of the Tertiary 

 period. H. Wincza. 'Ueber ein transitorisches Rudiment einer 

 knochernen Clavicula bei Embryonen eines Ungulaten.' — Morpliol. 

 Jahrbuch. xvi. p. 647. 1890. 



