AJIBLYPODA. 603 



feet 3- or 5-toed ; vertebrarterial canal pei'forating neural arches of cervical 

 vertebrae. Tertiaries of S. America. Theosodon Am., orbit open behind, 

 manus and pes vdth 5 digits, the outer being much reduced ; Eocene, 

 Patagonia. Macrauchenia Ovv., manus and pes with three digits, orbit 

 closed ; femur with third trochanter ; Miocene and Pliocene S. Amer. 



Fam. 2. Proterotheriidae. Nasal bones elongated, orbit closed, dentition 

 i \ c j{ p ^ m i|, with short diastema, grinders resembling those of 

 Anchitherium. Limbs 3- to 1-toed, the lateral metapodia weak. Tertiaries 

 of S. America. Pr oter other ium Amegh., Eocene, Miocene, S. Amer., with 

 3 toes. Thoatherlum Am., with one toe, Eocene, Patagonia. 



Order 9. AMBLYPODA.* 



Extinct semiplantigrade animals with pentadactyle hoofed 

 limbs, interlocking carpals and tarsals, and very small brain. 

 There is no clavicle. A centrale is sometimes present in the carpus 

 and aii cntepicondylar foramen in the humerus. The grinders are 

 lophodofit, and usually brachyodont. 



We separate this order very doubtfully from the Ungulata. It 



presents most of the ungulate features, and the grmders are 



ungulate-like. The most remarkable character of the group is 



the minute size of the brain which seems to separate it from all 



other mammals (Fig. 319, A). 



They are extinct, usually large, semiplantigrade animals with short, 

 hoofed, pentadactyle feet and broad terminal phalanges (Fig. 319). The 

 dentition is usually complete, and the grinders are brachyodont and 

 lophodont. The brain is very small and smooth, smaller and simpler than 

 in any other known mammal. The orbit is open behind. The ulna and 

 fibula are free and well developed. The carpalia alternate slightly and 

 a centrale is sometimes present, the astragalus is flattened and articulates 

 largely with the cuboid and with the tibia and fibula, and the femur has 

 a third trochanter only in the earlier forms. There appears to be no 

 clavicle, but the scapula has a large acromion. There is an entepicondylar 

 foramen in Pantolambda, but not in the more recent forms. The Amblypoda 

 present a certain resemblance to the elephants in their size, feet and 

 the general structure of their limbs ; but the resemblance is only super- 

 ficial. The head and dentition of the two groups differ totally, and the 

 resemblance in the limbs is quite superficial. For instance there is no 

 interlocking of the carpal and tarsal bones in the elepliant, and the astraga- 

 lus is quite different in shape in the two groups. Moreover the elephant 

 has no third trochanter. They are found in Europe and America and are 

 confined to the Eocene. The earliest forms are from the Lower Eocene. 

 Pantolambda Cope, L. Eocene, New Mexico, of moderate size, dentition 

 complete, grinders tritubercular, skull without horns, femur with third 



* Cope, The Ainblypoda, Amer. Nat., 1884 and 5. Earle, Revision 

 of the species of Coryphodon, Bull. Amer. Mns. N. Hist., 4, 1892. Marsh, 

 Monograph of the Dinocerata, U. S. Geol. Surv., 10, 1884. Osborn, Bull. 

 Amer. Mus. N. Hist., 10, 1898. 



