150 SHUFELDT. 



Before completing our study of the basis cranii, it wiU be as well to 

 finish with the teeth, and to this end examine those of the mandible or 

 the lower jaw. For this purpose one of the specimens (2) from the 

 Bureau of Science will be used, as in it the dental armature is unusually 

 perfect. (Plate I, figure 2.) This specimen presents other interesting 

 features, for on the right side there is to be noted the eruption of a 

 second canine tooth immediately external to the canine belonging to the 

 full set. The former is closely pressed against the latter and is nearly 

 of equal size, although only about two-thirds of the crown has made its 

 appearance. A similar eiiiption is seen in the case of both second 

 premolars. At the outer side of each, but not in contact with them, a 

 minute cusp is making its appearance just within the alveolar margin. 

 This is another second premolar struggling to the surface. The anterior 

 cusp of the first premolar in this jaw closely resembles the canine next 

 in front of it; the crown of the second premolar possesses characters very 

 much like those of the first true molar, but the cusps are a trifle longer 

 and sharper than they are in the latter. 



Six perfect incisors are found in this specimen, three in either side 

 of the mandible. The two pairs in front very closely resemble each other, 

 while the last incisor upon either side is quite different. All are single 

 fanged, and in the dried slcuU easily tumble out of their sockets. In 

 this particular they markedly depart from the molars, which require 

 some little force to extract them with the fingers. Owen, in his above- 

 cited figure of a section of one of the first incisors of the lower jaw, 

 makes seven elongate pectinations on the tooth, while in the four now 

 being considered, there are at least eleven of these structures. The 

 crowns of the two central incisors are somewhat narrower than in the 

 pair to their outer sides, otherwise, as has been remarked, they are 

 similar. The exp)0sed part of the tooth in any case is nearly square in 

 outline. As normally implanted the teeth point almost directly forward ; 

 that is, their anterior and posterior surfaces, including the cutting edges, 

 lie almost in the horizontal plane, and, excepting prehension, it is difficult 

 to understand the use for which they can be employed. In young 

 specimens these four iucisors are of a glistening, enamel white, while iu 

 old age they become stringy and flexible. Each is gently concave on 

 its inner (here upper) aspect, and correspondingly convex on its outer 

 surface or, in reality, its inferior surface. Owing to their pectination, 

 the free distal edges are minutely serrated. The pectinations are of 

 nearly uniform lengih, the proximal ones being the shortest in any 

 particular tooth. They are subcylindrieal in form, extremely delicate in 

 structure, although very strong, and it requires a lens of some power to 

 reveal the fact that the interstices among them are carried down to their 

 bases; distally, they are ajjparently in close contact, but not fused. No 

 other li^'ing manunal possesses such teeth as these. 



