TIIK MAMMALIA OF THE LINT A FORMATION. 5(51 



tion of the lateral tlij^its in the ungulate foot is largely the direct result of elevation 

 to the uuguligrade position which rendered useless the shorter lateral digits of the 

 plantigrade foot. Yet every step in reduction of the toes inlUienced the growth and 

 displacement of the more proximal elements. 



It can be demonsti-ated that these three processes were concomitant, and while 

 resulting directly or indirectly from the same causes, wei-e not all'ected in the same 

 degree by them. The problem may be expressed in this way : What were the prin- 

 cipal factors in each of the above processes, and how did these processes interact. 



2. Theories of modijicaiion. As Kowalevsky was unaware of the primitive 

 serial arrangement of the podial elements, his studies were chiefly directed to the 

 phenomena of growth in the metapodials and the manner in which in the adaptive 

 and inadaptive artiodactyls and in the perissodactyls the second and third metacar- 

 pals spread from their respective carpals to the adjacent elements.* 



Kyder}- latei- pointed out the ettect of impacts and strains upon (he phenomena 

 of reduction of the digits. 



CopcJ the first to recogni/.e the common development of the ungulate foot from 

 a primitive serial type, was also the first to advance a "displacement" theory: " As 

 the foot is descending towards the ground it is with the distal part of the leg rotated 

 from within outwards. The rotation of the foot is promptly arrested at the moment 

 of its contact with the ground, and the efiect of this arrest is to produce a torsion of 

 the leg, and a pressure from within outwards of the proximal or moving element of 

 each articulation against the distal or fixed element." 



An adequate theory for the displacement phenomena must, however, explain the 

 shifting of the metacarpals and metatarsals, as well as that which takes place between 

 the two rows of carpals and tarsals. The latter always takes place (excepting in (he 

 Proboscidia) in the same direction. I'lof. Cope's theory has thei'cfore to meet the ap- 

 parently fatal objection that the arrest of rotation to the ectal side would be first felt 

 at the junction of the metapodials and podials, and if it were o[' tiie character he de- 

 scribes, would coiUinually tend to separate these joints and displace them (o the eiital 

 side, whereas v/e find them provided with facets to resist pressure towards the ectal 

 side. 



It is a significant fact, recently pointed out by Weithofer,!^ that in all ungulates 

 in which the radius is larger than (he uln.i, the proximal row of cari)als is displaced 



• Monog. dcr Gait. AntbraroUieriiiin, IHTH, p. 142. 



fOnUie Laws ot" Diirital liccliirlinn. Aniericnn Nnliirali^l, 1H77, p. *W^. 



tThc PerisaoOurlylii. American Niiluralist, IH-ST. p. 980. 



§ Einigc BcmcrkiingcD iibcr (IcD Carpus dur Probosc'iOicr. K Aiil. WcillinliT, Murpli. .lulirl"., 1888, p. 508. 



