RHINOCEROS. 87 



entire ; and it contains all the molar teeth, which have their crowns worn nearly 

 to a level with the alveolar margin. (XV. 1, 2.) From Dr. Owen's collection. 



4. The crowns of four permanent premolars of the left side of the upper jaw 

 and one of the right side. These are perfect and are not at all worn, having been 

 concealed within the maxillary bones, from which they were removed with much 

 labor. (XIV. 4-8.) Presented to the Academy of Natural Sciences, by Mr. 

 Alexander Culbertson. 



5. A small fragment of an upper jaw containing the first permanent true molar, 

 slightly worn, and a portion of the fourth permanent premolar, which was still 

 concealed within the bone. From Dr. Owen's collection. 



6. A small fragment of an upper jaw, with an unworn sixth molar, and the 

 seventh unprotruded. From Mr. Culbertson's collection. 



7. A second inferior permanent molar, and two fragments of lower jaws. One 

 of the latter contains the fifth molar unworn, and the other contains a sixth molar 

 partially protruded. All three specimens are apparently from different individuals. 

 From Mr. Culbertson's collection. 



8. A fragment of the right side of a lower jaw, containing the last three molars. 

 From Dr. Owen's collection. 



9. A fragment of the left side of a lower jaw of a very young animal, containing 

 the last temporary molar unworn, and the first permanent true molar protruded. 

 (XIV. 9, 10.) From Dr. Owen's collection. 



10. A fragment of the right side of the upper jaw, containing the posterior three 

 temporary molars, which are considerably worn. (XIV. 14.) From Mr. Culbert- 

 son's collection. 



Description of the Head. — The skull of Rhinoceros Nehrascensis is about three- 

 fourths the size of that of Rhinoceros occidentalis. 



Lateral View. — (PL XIV. 1 ; XV. 1.) So far as can be ascertained from the im- 

 perfect specimens, the side of the head presents most of the characters of that of 

 Rhinoceros occidentalis. 



The root of the zygomatic process is implanted about the middle of the bottom 

 of the temporal fossa, and its upper surface is antero-posteriorly convex. 



The temporal surface is convex and smooth, and, as in Rhinoceros occidentalis, 

 apparently rose upon a prominent sagittal crest. Its occipital border curves from 

 the base of the mastoid process upward and backward to the summit of the inion. 



The squamous portion of the temporal bone is nearly vertically convex, and is 

 an inch in height above the root of the zygomatic process. 



The squamous suture at its upper part pursues a course almost horizontal for 

 nearly three inches. At its posterior part, in the particular specimen under investi- 

 gation, there are two deep, ascending, vascular grooves. 



The orbit has about the same form as in Rhinoceros occidentalis, but in the 

 specimens its floor is more superficial. 



The optic foramen is large and vertically oval, and is placed an inch in advance 

 of the spheno-orbital foramen. 



The margin of the orbital entrance is as well defined as in Rhinoceros occidentalis; 

 but the supra-orbitar process is neither quite so prominent nor so rough. 



