RUDIMENTARY STRUCTURES. 



239 



whole of the four metacarpals were large, and com- 

 pletely separate from each other; while all the four 

 toes were fully applied to the ground in walking. In 

 the Pigs, however, the outer (2nd and 5th) metacarpals 

 have become much reduced in size ; while their small 

 toes, as we may see any day for ourselves, only touch 

 the ground when the animal is walking on soft or 

 marshy ground. A still further dimi- 

 nution in the size of these lateral meta- 

 carpals is presented by the foot of the 

 extinct creature shown in Fig. 80, 

 where we find that they are only repre- 

 sented by small splints of bone (2 and 5) 

 occurring at the upper and lower ends 

 of the two middle metacarpals. In this 

 animal these middle metacarpals (3 and 

 4) still remain separate from one another, 

 but in the Deer, Sheep, and Cattle they 

 have become completely welded to- 

 gether to form a single bone, known 

 as the " cannon-bone." In some Deer FIG. so.-The bones of 



the upper part of 



the outer metacarpals are represented the foot, or meta- 



, ,. , j carpus, of an extinct 



merely by splints at the upper end or Even-toed ungulate 

 this cannon-bone, and in others by t Gelom ^ 

 similar splints at its lower end. In the Sheep and 

 Oxen the upper splints have totally disappeared, while 

 in the Giraffe both upper and lower splints are wanting, 

 so that the metacarpus is represented only by the 

 cannon-bone, composed of the originally separate 3rd 

 and 4th metacarpals. With this more or less complete 



