472 THE VERTEBRATE SKELETON. 



any considerable part of the side of the face, and the maxilla 

 commonly takes part in the formation of the zygomatic arch. 



TOXODONTIA. The skull in the Toxodontia shows several 

 Artiodactyloid features, while the manus and pes are of a more 

 Perissodactyloid type. The Artiodactyloid features are (1) the 

 absence of an alisphenoid canal, (2) the fact that the palate is 

 not excavated behind, and that the palatines form a consider- 

 able part of it, and (3) the fusion of the tympanic to the 

 squamosal and exoccipital, forming the floor of an upwardly 

 directed auditory meatus. The frontal has a fairly well deve- 

 loped postorbital process, but the orbit is confluent with the 

 temporal fossa. The premaxilla is well developed, as is the par- 

 occipital process of the exoccipital, especially in Typotherium. 

 The mandible has a rounded angle and a coronoid process of 

 moderate size. In Typotherium the ascending portion is very 

 massive. 



C ONDYLARTHRA. As far as is known the skull of these 

 generalised Ungulates is depressed, and is frequently marked 

 by a strong sagittal crest. The cranial cavity is small, the 

 cerebral fossa in Phenacodus being exceptionally small. The 

 orbit is completely confluent with the temporal fossa. 



HYRACOIDEA. The skull of Procavia resembles that of 

 Perissodactyles more than that of any other Ungulates, but 

 differs strongly in the comparatively small size of its facial 

 portion. The posterior portion of the cranium is rather high, 

 the occipital plane being nearly vertical. There is a small 

 interparietal. The nasals are wide behind, and the zygomatic 

 arch is strongly developed, its most anterior part being formed 

 by the maxilla. The jugal and parietal give rise to post- 

 orbital processes which sometimes meet, but as a rule the orbit 

 is confluent with the temporal fossa; it is very uncommon 

 for the parietal to give rise to a postorbital process, and even 

 in Procavia the frontal often forms part of the process. The 

 alisphenoid canal, and postglenoid and paroccipital processes 

 are well developed. The tympanic bulla is large and the 



