Another group of the Condylarthra contains the genus _Pertipychus_ and some others. _Periptychus_ has the full dentition {205} of forty-four teeth, the molars being of course bunodont, with the three chief tubercles most developed. The bones of the tarsus interlock and are not serial, as they are in many other members of the Condylarthra. The astragalus has a shorter neck than in _Meniscotherium_, for example. It has in this a likeness to the same bone in the Amblypoda, to the primitive members of which, such as _Pantolambda_, this animal bears much resemblance. "Astragali and many skeletal bones of _Periptychus rhabdodon_ and _Pantolambda bathmodon_ are almost indistinguishable," observes Mr. Matthew. The fore-feet of this genus are unknown, but it would seem that it was plantigrade from the evidence of the hind-feet. There are several species of the genus. Possibly, but not at all certainly, the Mioclaenidae, with the genera _Mioclaenus_ and _Protoselene_, are to be referred to this same order of primitive Ungulates. It is only necessary to mention them here, because they show very clearly the primitive form of dentition of these early Eocene mammals. The teeth are quite complete and unbroken by a diastema. The canines are but little pronounced. The molars are not strictly tritubercular, but have a prevailing trituberculy. The nature of the feet is not known. Since the genus _Protoselene_, as its name denotes, shows an indication of a commencing selenodonty, it has been suggested that this group is the stock whence the Artiodactyles have been derived. In any case, whether the particular comparisons that have been made as to the relationship of various forms of Condylarthra are valid or not, it seems to be plain that this group represents the earliest Ungulate stock, but little differentiated from the contemporaneous Creodonts. SUB-ORDER 2. AMBLYPODA. This group of extinct mammals has the following principal characteristics:-- They are large, semiplantigrade Ungulates, of heavy build and apparently elephantine gait. The dentition is for the most part complete as in other ancient groups, and the canines are in the later forms big tusks. The back teeth are brachyodont and ridged (lophodont). Both radius and ulna in the fore-limb, and tibia and fibula in the hind-limb, are well developed. The bones {206} in the carpus are alternating in position. The toes are five in both feet, and are very short. There is a hint of commencing "perissodactylism" in the fore-feet at any rate. The brain is small and the hemispheres smooth. The Amblypoda, or Amblydactyla, are so called on account of their short and stumpy feet and toes. They were held by Professor Cope to be on the direct line of ancestry of both Perissodactyles and Artiodactyles, a view which is on the whole not accepted at present. [Illustration] FIG. 114.--Skull of _Protolambda bathmodon_. x 3/4. _e.a.m_, External auditory meatus; _m_, mastoid; _m.f_, mastoid foramen. (After Osborn.)