2l6 



VERTEBRATE SKELETON 



NoTVNGVLATA.—Toxodon, the best known member, has a vertical occiput, 

 a brain case relatively larger than in recent Ungulates, a strong sagittal crest, 

 nares on the upper side of the snout, the narial passages being roofed by short 

 nasals which hardly extend in front of the posterior ends of the premaxillae. 

 Orbits and temporal fossae are confluent, a very strong zygomatic arch occurs 

 and the lacrimal is entirely within the orbit. Typotherium differs in the longer 

 nasals, an occiput inclined backwards and in having a facial part to the lacrimal. 

 Toxodon and Typotherium have rodent-like incisors. 



Hyracoidea (fig. 228) have a snout short in relation to the rest of the 

 cranium, a complete zygoma, and orbits far anterior, which are usually separated 

 from the temporal fossae by postorbital bars, partly frontal, more largely parietal 

 in origin. There is no sagittal crest, the occiput is nearly vertical and one or two 



Fig. 228. — Skull oi Procavia capensis (Weber, '04). a, alisphenoid; bo, basioccipital; 

 bs, basisphenoid; m, maxilla; n, nasal; pi, palatine; pm, premaxilla; ps, presphenoid; 

 pt, pterygoid; sq, squamosal; t, tympanic; 2, zygomatic. 



interparietals are present, while the parietals form most of the cranial roof. 

 The broad frontals roof the orbits and meet the broad nasals. The premaxillae 

 are short, and the maxillae (with diastemata) intervene between them and the 

 frontals. The zygomatic bone forms the lower border of the orbit and extends 

 back to form part of the transverse mandibular fossa. The perforate lacrimal is 

 small and, lying between maxilla and frontal, extends to the face. There is 

 an optic foramen, and foramina rotundum and ovale and an alisphenoidal canal 

 perforate the alisphenoid. 



The incisive foramina are almost surrounded by the premaxillae. The 

 petrosal, with a small mastoid part, is loosely connected with the tympanic. 

 Postglenoid and posttympanic processes are present, the paroccipital process 

 large. The symphysis of the mandible is low the bone being higher behind. 

 The hyoid is described as dififering from that of other mammals in having a trans- 

 versely oval basal part with which are articulated a pair of flat ceratohyals which 



