LEIDY'S OSTEOLOGY OF THE HEAD OF HIPPOPOTAMUS. 211 



slightly forwards, is quadrilateral, and has the external side convex and mvested by a 

 band of enamel, nine lines wide, and the other three sides longitudinally depressed. At 

 the postero-internal angle of the right mid incisor only, a band of enamel exists three- 

 fourths of a line wide. The triturating surface is quadrate, about one inch in 

 diameter, directed downwards, and a little obliquely towards that of the other side. 



The lateral incisors of the male are strongly curved, cylindroid, seven inches in 

 length, of which two and three-fourths are exserted, by four in circumference. They 

 are totally devoid of enamel, project from the jaw downwards, outwards, and towards 

 the distal end slightly backward, and are abraded upon each side for one and 

 three-quarter inches. 



In the female the lateral incisors above, project from the jaw downwards and 

 slightly inwards for one and a quarter inches ; are two inches seven lines in circum- 

 ference, and quadrilateral, with two broad flattened sides directed postero-external and 

 antero-internal, and two narrow convex sides, the antero-external of which is invested 

 by a band of enamel two and a half lines wide. Abrasion has given the protruded 

 portion of the tooth a conical appearance, with a blunt apex. 



The exserted portion of the superior canines of the male measure two and a half 

 inches externally and five inches two lines in circumference, at the border of their 

 alveolus. The posterior groove is broad and three and a quarter lines deep. The 

 anterior abraded surface presents two planes, one external and superior to the notch, 

 the other about one-sixth the size of the preceding, and internal to the notch. The 

 long diameter of the former plane is oblique, and measures two and a half inches. 



In the female the protruded portion of the upper canines externally is two inches 

 in length, and is four and a half inches in circumference at its base. The posterior 

 notch is much shallower than in the male, being a line only in depth. The anterior 

 abraded surface is constituted by one simple vertical reniforra plane, with the long 

 diameter oblique, and measuring two and a half inches. 



Comparison between Hippopotamus ampliibius and Hippopotamus Capensis. — Hippo- 

 potamus amphibius is a little smaller than Hippopotamus Capensis. The lower jaw 

 is less spreading posteriorly, less deep at the angle, and very much narrower 

 posteriorly. 



The parietal ridge of the male is shorter but thicker, and the orbits are much 

 smaller, more nearly circular, and less oblique in the same sex. 



The upper canines are more exserted, and those inferior, very much smaller. 



The mo.st remarkable difference exists in the arrangement of the enamel 

 of the superior canines. In Hippopotamus Capensis, in both sexes, old and' 

 young, the outer side of the posterior groove of the upper canine presents a space 

 uncovered by enamel, in the adult three lines wide; or, the enamel investment of the 

 tooth consists of two unequal bands, one covering the outer semi-circumference, the 



