CARPUS AND TARSUS OF ARTlOUACTYLES 



27 I 



the facts of Ungulate descent are absolutely destructive of any 

 such cmnparisons. 



As is the case with the Perissodactjdes, tlio ArticKlactyles 

 show a historical series, the primitive tive-toed condition being 

 almost preserved in Orrodon, up to the most modern modification 

 exemplified by the Ox, Shee}), etc., in which animals there are ni)t 

 even vestiges of the fourth and fifth toes. Tt has been stated, 

 however, that the foetal Sheep has traces of 

 those rudiments. The so-called cannon bone 

 (the fused third and fourth meta])()dia) is 

 accompanied in its fusion by an increase in 

 length. At the same time the functional 

 middle metacarpals push aside the rudiments 

 and, forming a broad surface for that purpose, 

 articulate with the magnum and unciform 

 l)ones to the exclusion of the rudiments. 

 This has been termed an " adaptive reduc- 

 tion." In the " inadaptive reduction " tliere 

 is the same reduction of the metacarpals, 

 l_)ut the rudiments still articulate as in the 

 primitive Artiodactyle foot, i.e. Mc II with 

 trapezium, trapezoid, and magnum ; Mc III 

 with magnum and unciform ; Mc IV and V 



with unciform. This would appear to give j,,,, 139. ^Dorsal surface of 



greater solidity and consequently greater 

 strength to the foot. 



The carpal bones of the Artiodactyla 

 alternate in their articulation ; the primi- 

 tive state of affairs ^ is not retained even 

 in the earliest types. The femur has no 

 third trochanter, so prevalent in the Perissodactyles. In the 

 hind-foot the calcaneum has an articular facet for the fibula, 

 which is not characteristic of the Perissodactyla. In the more 

 modern forms, e.g. the Cervidae, the navicular and culjoid become 

 fused into one bone ; and there are even further fusions which 

 will be referred to later as characteristic features of different 

 groups. It is interesting to notice that the reduction begins 

 earlier and is clearer in the hind-fcjot than in the fore. One 



right tar.sus of Red Deer 

 (Cerviis elaphus). x i. 

 II., Astragalus ; c, cal- 

 ciineuiu ; c\ cuneifonn ; 

 rh, cuboid ; mill, luJV, 

 metatarsals ; n, navicu- 

 lar. (From Flo\ver'.s 

 OsteoJoijij. ) 



^ See, however, p. 196, for a discussion a.s to which is the more iirimitive 

 arrangement. 



