18 DINOCERATA. 



thicker, and swell into a distinct prominence, whicb afforded protection to 

 the eye below. From this point back to the posterior protuberances, or 

 horn-cores, the lateral margin of the frontal is thickened into a strong 

 crest, which rises nearly to the sunuiiit of the elevations, leaving a distinct 

 notch where they terminate. This depression marks the position of the 

 fron to-parietal suture, here entirely obliterated. 



On tlie side of the cranium, the frontal bones are bounded anteriorly 

 by the maxillary above, and, lower down, by the lachrymal, as shown in 

 Plate II. Further back on the top of the skull, the frontals are depressed, 

 forming a deep concavity, the lowest portion of which is usually in front of 

 the brain-case. In the posterior portion of the frontals, there are numerous 

 air cells, which materially lighten these bones in this part of the cranium. 



The Parietal Bones. 



In all of the crania of the Dinocerata examined, the parietal bones are 

 firmly united to each other on the medial line, and with the supra-occipital 

 behind. In the single young specimen already mentioned (number 

 1601), the anterior border of these bones is distinctly marked by sutures, 

 as shown in figure 8, page 15. The large posterior protuberances, or 

 horn-cores, are thus mainly on the parietal bones, and the lateral crest, 

 behind these elevations, appears to be also composed of the parietals. 

 These bones are thick and massive, especially over the brain-case, but like 

 the frontals are lightened somewhat by air cavities, as shown in figure 35, 

 page 31. Between the osseous elevations, or horn-cores, on the parietals, 

 there is a distinct transverse ridge, which strengthens this part of the 

 cranium, and partially divides into two portions the deep concavity 

 enclosed by the lateral and posterior crests. On the sides of the cranium, 

 the parietals form the upper portion of the large temporal fossae. The 

 suture between the parietal and squamosal below may often be distinctly 

 made out, as shown in Plate II. The share of the parietals in the lofty 

 occipital crest, cannot, at present, be determined with certainty, as here, 

 even in the youngest specimens known, the sutui'es are obliterated. 



