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 paleontologists 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. Leriptychus, 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 Phenucodus, 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- 
therinm 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 Hyracotherivm , all the feet had 
five fully developed digits, and the tail was long. J/eniscotherinin 
and Hyracodontotherium are more specialised forms of somewhat 
later age, with a lophodont dentition; the latter genus heing 
European. 
Suborder TOXODONTIA. 
In addition to'the Macraucheniide and certain other forms 
noticed under the head of the Perissodactyla, the Tertiarics 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 Torodon.—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- 
therium (p. 412) and the following genus Toxulon, The typical 
species of Nvsodon was about as large as a Sheep, but nothing 
more is known of it than the teeth and portions of the skull. 
Tocodon 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 «3, ¢ 2, p 4, m #= 38. 
