AMBLYPODA. 
180 
invested Avitli enamel, with wide crowns and transverse crests. A post¬ 
glenoid process. 
The above characteristics are the only ones which can, in the author’s 
estimation, be admitted into the ordinal category, for although the animals 
embraced in the AmNf/jmla present many other peculiarities, they are such 
as may readily vary within the limits of an order, and in fact do so in the 
families of many of the orders knoAvn to us. The above definition displays 
a double set of affinities, viz: those indicated by the structure of the feet, 
and those expressed by the type of the brain. The former exhibit the 
closest resemblance to the feet of the Proboscidian the approach being 
greatest in the hind foot. The principal difference in this extremity is seen 
in the extension of the navicular articulation over the entire distal end of 
the astragalus in the Proboscidian while in the Amblypodan the navicular is 
shortened, thus permitting the cuboid to come in contact with the external 
part of the distal extremity of the astragalus. The cuboid is alike in the 
two orders, having considerable transverse extent, and supporting the 
external two metacarpals on its distal face. This lengthening of tlie 
navicular is a specialty of the Proboscidia among hoofed Mammals, the 
■ shorter form being characteristic of the lower types of both Perissodactyla 
and Artiodactylan Avhere the astragalus has two distal articulations. In the 
Perissodactylan the extent of the navicular increases until the highest genus, 
the Horse, is reached., where it almost covers the entire end of the astraga¬ 
lus; but, in the Artiodactylan the extension of the cuboid over the astragalus 
does not diminish. The nearest approach to the distal articulation of the 
astragalus of the Amblypodan outside of the order, is seen in the Miocene 
Perissodactyle genus Symborodon. Here the cuboid and navicular facets 
are flat, and separated by an oblique line, so as to be similarly incapable 
of hinge-like movement. The resemblance to the loAvest Artiodactyla (e. ^., 
Oreodorin Hippopotamus) is very remote, for there the two facets are parallel, 
offering a ginglymus to the articulating bones. 
The difference betAveen the fore foot of the Amblypoda and that of the 
Proboscidia consists in the alternating position of the elements of the tAvo 
carpal rows. This is also a character of the two other living orders of 
