1882.] 440 [Cope. 



III. AMBLYPODA. 



The sub-orders of this order, as I pointed out in 1873, are two, defined 

 as follows : 



Superior incisor teeth ; no ali-sphenoid canal ; a third trochanter of femur ; 



Pantodonta. 

 No superior incisors, nor ali-sphenoid canal, nor third trochanter of femur ; 



Binoceratd. 



The difference between the Proboscidea and the Amblypoda consists 

 chiefly in that the navicular of the latter is shortened externally so as to 

 permit the cuboid to articulate with the astragalus. The cuboid has the 

 same form in both. The peculiar character of the navicular gives the 

 astragalus a different form. 



IV. DIPLARTHRA. 



This order is called by some authors the Ungulata, but that name is also 

 used in the larger sense in Avhich it is here employed. This appears to be 

 its legitimate application, as the name should, if possible, be used for hoofed 

 Mammalia in general, as its meaning implies. The two well known sub- 

 orders are the following : 

 Astragalus truncate distally ; number of toes odd, the median one the 



largest Perissodactijk' . 



Astragalus with a distal ginglymus ; number of toes even, the median two 

 largest Artiodactyln . 



Phylogeny. — The serial arrangement of the bones of the carpus and 

 tarsus seen in the Taxeopoda, is probably the primitive one, and we may 

 expect numerous accessions to that order on further exploration of the early 

 Eocene epochs. The modification seen in the more modern orders of 

 Perissodactyla and Artiodactyla, may be regarded as a rotation to the inner 

 side, of the bones of the second carpal row, on those of the first. This 

 votation is probably nearly coincident with the loss of the pollex, as it 

 throws the weight one digit outwards, that is on the third and fourth 

 digits, rendering the first functionally useless to a foot constructed solely 

 for sustaining a weight in motion. The alternation of the two rows of 

 carpals clearlj' gives greater strength to the foot than their serial arrange- 

 ment, and this may probably account for the survival of the type possess- 

 ing it, and the extinction ot nearly all the species of the type which does 

 not possess it. Here is applied again the principle first observed by 

 Kowalevsky in the proximal metapodial articulations. This author shows 

 that the types in which the metapodials articulate with two carpal or tarsal 

 l)ones, have survived, while those in which the articulation is made with 

 a single carpal or tarsal have become extinct. The double articulation is, 

 of course, mechanically the more secure against dislocation or fracture. 



As regards the inner part of the manus I know of no genus which 

 presents a type of carpus intermediate between that of the Taxeopoda and 



