182 
AMBLYPODA. 
cerebral develoj)ment in both the clawed and hoofed types of Eocene 
Mammalia. 
As a resume of the relations of the Aml)hjpoda, it may be said that 
they are the most generalized order of hoofed Mammalia^ being interme¬ 
diate, in the structure of their limbs and feet, between the Prohoscidia, the 
Perissodactyla, and the Artiodactyla. This fact, together with the small size 
of the brain, places them in antecedent relation to the latter, in a systematic 
sense, connecting them with the lower Mammalia with small and smooth 
brains, still in existence; and, in a phylogenetic sense, since they preceded 
the other orders in time, they stand in the relation of ancestors. It is 
doubtless true that the Amhlypoda were the ancestors of all living Ungu¬ 
lates, although no genus of the latter can yet be traced to any known 
genus of the former, such genera remaining for future discovery.* Standing 
in this antecedent relation, comparison with other classes of Vertehrata is 
in place. The proportionate size of the brain is, as has been discovered by 
Marsh in the Dinocerata, more like that characteristic of many Eeptiles than 
of Mammals, and I may add that the immovable tibio-tarsal articulation is 
a Eeptilian feature as well. These are, however, but hints of a relationship 
doubtless very remote. 
Before proceeding to a more detailed consideration of the genera of 
this order, I give the distinguishing characteristics of the two suborders 
into which they naturally fall: 
I. A third trochanter of the femur, and fossa for the round ligament; no 
alisphenoid canal; superior incisors present. Pantodonta. 
II. No third trochanter nor fossa for the round ligament; an alisphenoid 
canal; no superior incisors. . Dinocerata. 
The differences presented by these suborders are thus very decided, 
but they agree in some important points, not necessarily of ordinal value. 
Thus tlie foramen ovale is distinct from the foramen lacerum anterius, and 
the meatus auditorius is not closed inferiorly. In the first point, they agree 
with Symhorodon and PMnocerus more than with any Prohoscidia or Artio- 
*A discussion of these and other general relations of the Amhlypoda may be 
found in a paper read by me before the American Association for the Advancement of 
Science, August, 1875, and published in the Penn Monthly Magazine, December, 1875. 
