560 SUMMARY OF CUERENT RESEARCHES RELATING TO 



toes are rudimentary from their very start; the lateral toes appearmuch 

 thinner and shorter than the middle toes, even in the earliest stages 

 when the first toe still exists. Only in the much greater reduction of 

 the first toe do we find an indication of the fact that in the history of 

 i he limb it was reduced at much earlier date than the lateral digits. 



Metacarpal n and the trapezoid, metacarpal iv and the unciform, 

 metatarsal iv and the cuboid, form single rays in their earliest primordia, 

 and there is a subsequent separation of the' carpal or tarsal element from 

 the metapodial. This could not be represented in the phylogenetic 

 series, being for mechanical reasons impossible. As a mode of develop- 

 ment it is well known in reptiles. When metacarpal n is separated off 

 from the trapezoid, it remains directed towards the trapezoid, and to it 

 only, a characteristic of the adaptively reduced extremity. It becomes 

 subsequently shunted to the volar side of the median metapodials. 



The specializations of the limb of Sus occur ontogenetically very 

 much in the same succession as those of Bos, and in a similar relation 

 to the palajontological series. Noteworthy are the relations of the second 

 metapodial element in both limbs. Metacarpal II is at first connected 

 with the trapezoid ; later on the two elements are separated, then the 

 metacarpal n is shunted first in the direction of the axis of the limb and 

 then back towards the median margin. The position of metacarpal n 

 shows the following stages : (1) association with trapezoid, (2) relation 

 with the os magnum as well, and (3) a connexion with the trapezoid 

 (and trapezium), but not with the magnum, which is wholly occupied by 

 the third metacarpal. The second stage marks a condition of non- 

 adaptive reduction, the third of adaptive reduction. 



Similar conditions obtain in the hind leg. The second metatarsal is 

 laid down in connexion with the second cuneiform. Then it is separated 

 off and shunted laterally, becoming directed to the third cuneiform. 

 Finally, it comes back again to the second cuneiform, the third being 

 wholly occupied by the third metatarsal. The second stage marks 

 non-adaptive, the third adaptive reduction. 



These movements of the second metapodial ray seem to be quite 

 unnecessary for the attainment of the final result. In Bos they do not 

 occur, and the first position is the final one. The movements can hardly 

 be referred to purely developmental conditions, e.g. to strong growth of 

 the third metapodial. This might compel the second metapodial to its 

 final position, but the lateral movement remains unexplained. It is 

 probable that an explanation is to be found in the phylogeny, i.e. in the 

 assumption that Sus in its phylogenetic history passed through a primary 

 non-adaptive stage, such as may be seen in Ghm other ium in the fore 

 limb. In Amniota generally the hind limb appears to change more 

 rapidly in phylogeny than does the fore limb. It may be said that the 

 ontogeny of Sus compared with that of Bos shows more traces of the 

 primitive serial arrangement of the basipodium. 



The astragalus seems to represent the intermedium. At the end of 

 the tibia, in the position of a tibiaie, there is no proximal element laid 

 down. _ It is only subsequently that the astragalus, gets pushed into or 

 grows into this position. No centrale carpi was to be found. Some 

 elements of the metapodium are, in their primordium, in union with 



