358 THE VERTEBRATE SKELETON. 



adult except in a few generalised extinct forms such as Typo- 

 ihsrium, and it is only recently that vestigial clavicles have 

 been discovered in the embryo 1 . The scaphoid and lunar are 

 always distinct. 



The order Ungulata may be subdivided into two main 

 groups, Ungulata vera and Subungulata. 



Section I. UNGULATA VERA S . 



The cervical vertebrae except the atlas are generally opis- 

 thocoelous. The feet are never plantigrade*. In all the 

 living and the great majority of the extinct forms the digits 

 do not exceed four, the first being suppressed. In the carpus 

 the os magnum articulates freely with the scaphoid, and is 

 separated from the cuneiform by the lunar and unciform. In 

 the tarsus the cuboid articulates with the astragalus as well as 

 with the calcaneum, and the proximal surface of the astra- 

 galus is marked by a pulley-like groove. All the bones of 

 the carpus and tarsus strongly interlock. These characters 

 with regard to the carpus and tarsus do not hold in Macrau- 

 chenia and its allies. The humerus never has an ent-epicon- 

 dylar foramen. 



The group is divided into two very distinct suborders : 



Suborder (1). ARTIODACTYLA. 



The Artiodactyla have a number of well marked charac- 

 ters, one of the most obvious being the fact that many of the 

 most characteristic forms have large paired outgrowths on the 

 frontal bones. These may be (1) solid deciduous bony antlers, 

 or (2) more or less hollow bony outgrowths which are sheathed 

 with permanently growing horn. 



1 H. Wincza, Morphol. Jahrb. xvi., p. 647. 



2 See M. Pavlow, "Etudes sur 1'histoire paleontologique des Ongules." 

 Bull. Soc. Moscow, 18871890. 



3 In a plantigrade animal the whole of the foot is placed on the 

 ground in walking. A digiti grade animal places only its toes on the 

 ground. An intermediate condition is distinguished by the term sub- 

 plantigrade. 



