114 



SKETCH OF THE HISTORY OF MAMMALIA. 



The skull in question equals in size that of the hip- 

 popotamus, measuring two feet four inches in length, 

 and one foot four inches in extreme breadth. The form 

 of the skull (Figs. 70, 71) is elongated and depressed ; 

 the zygomatic arches are of enormous size and strength, 

 an index of the great volume of the temporal and mas- 

 seter muscles. The occipital region (Fig. 72) slopes 

 from the condyles upwards and forwards. The maxillary 

 ])ortion of the skull is compressed laterally, narrow 

 across, and with large intermaxillary bones, slightly 

 dilated at their extremity. The superior part of the 

 skull was cavernous, with cells, or sinuses, giving to it 

 greater apparent volume than the cerebral cavity would 

 lead us to infer. According to Professor Owen the 



4 

 dental formula is as follows : Incisors, ^ ; canines none, a 



vacant space being in their place ; molars, 



7—7 

 7—7 



38. 



74. — Incisor of Lower Jaw of Toxodon. 



The incisor teeth (see Fig. 73, the fragment of the an- 

 terior part of the lower jaw, with the teeth in situ; 

 and Fig. 74, an incisor of the lower jaw) are remarkable 

 for their resemblance in many respects to those of the 

 Rodents ; they were rootless, and had persistent pulps ; 

 growing, therefore, as worn down by use. In the upper 

 jaw the two central incisors were very small ; the two 



