580 



UNGULATA. 



skeletal parts of digits which are totally missing in the adult 



have so far been discovered in the embryo. 



The stomach is generally complex, the caecum small, the 



placenta diffused or cotyledonary. The mammae are few and 



inguinal or numerous and abdominal. 



The Artiodactyla constitute by far the largest group of living 



Ungulates. They are rich in genera and species and they are 



found all over the world except in Australia and New Zealand. 



The living forms are divisible into quite well defined groups, but 



there are a large number 

 of extinct forms, which 

 tend to fill up the gaps 

 between existing families 

 and to obliterate the divid- 

 ing lines. The earliest of 

 these are found in the 

 Eocene. 



Fam. 1. Suidae.* Skin hairy; 

 with tuberculated brachyodont 

 molars ; with incisors and 

 canines in both jaws ; the last 

 molar in both jaws with an 

 additional hinder lobe, the 

 premolars with a simple cutt- 

 ing edge ; the first deciduous 

 molar is not replaced. Four 

 completely developed digits in 

 both limbs, digit 1 being ab- 

 sent ; digits 3 and 4 are larger 

 than the others, are closely 

 applied together and the 

 adjacent surfaces of their 

 hoofs are flattened ; digits 2 

 and 5 do not reach the ground in walking. The metacarpals and 

 metatarsals are generally separate and never completely fused together. 

 The axis of the face is bent upon the basi-cranial axis ; the orbit 

 is not closed behind, the postorbital processes of the frontal and jugal 

 not meeting ; the openings of the lacrymal canal are on the face ; 

 the nasals are long and the premaxillae unite with them for some 

 distance ; there is often a prenasal bone ; the bulla is large, the bony 

 auditory meatus is long ; the post-glenoid and post-tympanic processes 

 of the squamosal are united beneath the meatus, and there is a long par- 

 occipital process. The centra of the cervical vertebrae are short. The 



* H. v. Nathusius, Die Racen des Schweines, I860, and Vorstudien 

 fur Oeschichte u. Zucht der Hausthiere, Berlin, 1864. Marsh, Homacodon, 

 Amer. Journ. Sci. (3), 48, 1894, p. 261. Filhol, Listriodon, Bibl. Ecol'e 

 Haute* Etudes, 37, 1890, t>. 205. 



JV T- 



FlG. 298. 



FIG. 298. Bones of the maims of the pig (Sus 

 scrofa) x (from Flower), digits numbered, 

 bones with initial letters. 



FlG. 299. Right tarsus of pig x %, 



