TOXODONTIA 439 



entepicondylar foramen ; the femur has a third trochanter ; and 

 the form and relations of the astragalus are similar to those obtain- 

 ing in the Carnivora. The feet are usually furnished with five 

 functional digits, of which the ungual phalanges are pointed. In 

 many respects the skeleton of these remarkably generalised Ungu- 

 lates approximates so decidedly to a Carnivorous type as to have 

 led palaeontologists to conclude that the Ungulata and Carnivora 

 are branches of an original common stock. 



In this work space only permits of allusion to a few of the 

 more important types of this group. Periptychus, which occurs in 

 the lowest Eocene of New Mexico, is a bunodont type readily dis- 

 tinguished by the vertical flutings of the premolars, and the small 

 size of the incisors and canines. It has been suggested that this 

 genus is closely related to the stock of the bunodont Artiodactyla. 

 Of greater interest is the genus Phenacodiis, which is regarded as the 

 lowest factor in the series from which the modern Horse has been 

 evolved, where it holds the position immediately below Hyraco- 

 therium or Systemodon (see p. 374). One of the species was about 

 the size of a Bull-dog, while another might be compared to a small 

 Leopard. The structure of the cheek-teeth is such as might readily 

 be modified into that obtaining in Hyracothenum ; all the feet had 

 five fully developed digits, and the tail, was long. Meniscotherinm 

 and Hyracodontotherium are more specialised forms of somewhat 

 later age, with a lophodont dentition; the latter genus being 

 European. 



Suborder TOXODONTIA. 



In addition to the Macraucheniidce and certain other forms 

 noticed under the head of the Perissodactyla, the Tertiaries of 

 South America have yielded some very remarkable forms of mam- 

 malian life, the nature and affinities of which have greatly puzzled 

 all zoologists who have attempted to unravel them. 



Nesodon and Toxodan. Among these Nesodon, from Patagonia, 

 has the full typical Eutherian number of teeth ; the crowns of the 

 incisors being short, and the molars having a complex rhinocerotic 

 type of structure somewhat intermediate between Homalodonto- 

 iheriwn (p. 412) and the following genus Toxodon. The typical 

 species of Nesodon was about as large as a Sheep, but nothing 

 more is known of it than the teeth and portions of the skull. 



Toxodon is an animal about the size of a Hippopotamus ; it was 

 first discovered by Darwin, and many specimens have since been 

 found in Pleistocene deposits near Buenos Ayres, and described by 

 Owen, Gervais, and Burmeister. The teeth consist of large incisors, 

 very small lower canines, and strongly curved molars, all with 

 persistent roots, the formula being apparently i |, c %,p ^, m $ = 38. 



