THE SKULL. 



17 



Tn this young specimen, tlie tVonto-parietiil suuire i.s hitill open, and 

 passes in a nearly straight line across the toj) of tlic cranium just in front 

 of the summit of the cerebral hemispheres. It also divides the posterior 

 elevations, or horn-cores, so as to leave the anterior part of them on the 

 frontals, and the posterior and liiyhest ])ortion on the parietals. In all the 

 other known specimens, this suture is nearl}' or quite obliterated, but 

 distinct traces of it are seen in several crania in the Yale Museum. 



FiGCRK 1 1. — .-^Iviill ol i'adui :i:riuin tati/iuns, Marsh (No. 1231); seen from aliove. 



Figure J 2. — Same view of skull of Tinoceras vagans. Marsh (No. 1241 ). 



/. frontal bone ; »«. ma.\illary bono; ?«'. maxillary protuberance ; m. nas 1 buue; n'. nasal protuberance 

 p. parietal bone ; p'. parietal protuberaneo ; pm. premaxiUary bono ; s. supraoccipital crest. 

 Both figures are one-eighth natural size. 



The position of this suture, and also that uniting- the frontals with the 

 nasals, and the latter with their adjoining bones, is well shown in figure 8, 

 page If), which represents the young specimen (number ItlOl) above 

 referred, to. 



In Diitoceras iiiij'alji/c (number lO.'W!), the frontals are comparatively 

 thin in front where they join the nasals. Over the orljits, thev become 

 3 



