286 ANATOMY OF VERTEBRATES. 



tion of the medullary artery at the fore and upper part of the 

 shaft, as in the Hippopotamus, the Hog, and most of the Rumi- 

 nants. The fore part of the astragalus is divided into two 

 equal or sub-equal facets : the os magnum does not exceed, or 

 is less than the unciforme, in the carpus; and the ectocunei- 

 form is less, or not larger, than the cuboid, in the tarsus. The 

 dio'it answering to the third in the pentadactyle foot is unsymme- 

 trical, and forms, with that ansAvering to the fourth, a symmetrical 

 pair. If the species be horned, the horns form one pair or two 

 pairs ; they are never developed singly, of symmetrical form, from 

 the median line. The post-tympanic does not project downward 

 distinctly from the mastoid, nor supersede it, in any Artiodactyle ; 

 and the paroccipital always exceeds both those processes in length. 

 The bony palate extends further back than in the Perissodactyles ; ^ 

 the hinder aperture of the nasal passages is more vertical and 

 commences posterior to the last molar tooth. The base of the 

 pterygoid process is not perforated by the ectocarotid artery. 

 The croA\^s of the premolars are smaller and less complex than 

 those of the true molars, usually representing half of such croAvn. 

 The last milk-molar is trilobed. 



To these osteological and dental characters may be added some 

 modifications of internal structure, as, e.g., the complex form of 

 the stomach in the Hippopotamus, Peccari, and Euminants ; the 

 comparatively small and simple cascum and the spirally folded 

 colon in all Artiodactyles. The placenta is diffused in the 

 Camel-tribe, Chevrotains,^ and Non-ruminants ; is cotyledonal in 

 the true Ruminants. The oldest known Artiodactyles were non- 

 ruminants, and from eocene beds. Many of the extinct genera, 

 e. g. Cheer opotamus, Anthracotherium, Hyopotamus, Entelodon, 

 Dichodon, Merycopotamus, Xipliodon, Diclwbujie, A?ioplotherium, 

 Microtherium, &c., linked together the now broken series of 

 Artiodactyles, represented by the existing genera, Hipjwjmtamus, 

 Sus, Dicotyles, Camelus, Auchenia, Mosclms, Camelopardalis, 

 Cervus, Antelope, Ovis, and Bos. 



A well-marked, and at the present day very extensive subor- 

 dinate group of the Artiodactyles, is called Ruminantia, in refer- 

 ence to the second mastication to which the food is subject after 

 having been swallowed ; the act of rumination requiring a pecu- 

 liarly complicated form of stomach. The Ruminants have the 

 ^ cloven foot,' i.e. two hoofed digits on each foot forming a sym- 

 metrical pair, as by the cleavage of a single hoof; in most species 

 two small supplementary hoofed toes are added, fig. 166, sp. 

 • Lxxr. p. 399. ^ CCXXXY1-. vol. ii. p. 135j and Lxxir. 



