THE SKULL. 



15 



of two separate ossifications, each in front of its respective nasal bone. 

 In figure 5, page 13, they are shown in position, with the sutures uniting 

 them to the nasals, and to each other. These bones ai-e a peculiar 

 feature in the skull of Dinocerafa, and niay be called the pre-nasal bones. 

 In A^ery young animals, they are unossified; in adult animals, they are 

 distinct, as in the specimen figured ; but in very old animals they 

 become co-ossified Avith the nasals, and with each other. 



Fig. 7. 



FKiURE 7— Skull oC Dinnceios mirabile. Marsh (No. 10:!6); with brain-cast in mtiiral position seen from ibove. 

 Figure 8. — The same view of a young specimen of Diuocerus distans, Marsh (No IbOl) 



/■. frontal bone ; m. maxillary bone; in', maxillary protuberance ; «. nasal bone; n'. nasal protuberance; 



p. parietal bone ; p'. parietal protuberance; pm. premaxillary bone; s. supra-occipital crest. 

 Both figures are one-eighth natural size. 



When separate, they are subquadrate in form, flattened on the median 

 line where they meet each other ; and rugose posteriorly, for sutural union 

 with the nasals. These ])re-nasal bones appear to be homologous with 

 the ossicle sometimes found at the extremitj' of the snout in suillines, 

 especially in the genus Siis. ^ 



