OSTEOLOGY 123 



trait is given by Goldman (1910) as a subgeneric character, 

 but it is quite variable and does not seem entirely reliable. 



In this postero-external reentrant angle is first found, in 

 the case of animals in the prime of adulthood, a develop- 

 ment which may occur in practically every other angle as 

 senility of the individual advances. This consists of a 

 segregation of the apex of the angle into an island of dentine 

 entirely surrounded by enamel (see fig. 26), and the final, 

 though not immediate, obliteration of all signs of the angle as 

 such upon the external, or lateral, surface of the tooth. 

 This is caused by the fact that the reentrant angles extend 

 deeper vertically in the central portion of the teeth than 

 along the margins, so that after the teeth are much worn, 

 the bases of the angles are obliterated sooner than the 

 apices. 



The first of the lower molars has three enamel spaces, and 

 normally two inner and two outer reentrant angles. In some 

 individuals the antero-internal angle is lightly defined, and 

 an accessory reentrant angle may be indicated upon the 

 antero-internal border of the first enamel space. The second 

 molar also has three enamel spaces, two internal and two ex- 

 ternal reentrant angles. The postero-external one of the 

 latter is the first to become isolated by wear. The third 

 molar is formed of two enamel spaces and a reentrant angle 

 upon either side, the external one of which is the first to be- 

 come isolated by wear. The third molars, both above and 

 below, are cut much later than the remainder of the cheek 

 teeth. 



HYOID 



The hyoid bone consists of a transverse body, with a 

 slight, mediocranial projection, two greater cornua, which 

 are a trifle shorter than the transverse measurement of the 

 body, extending latero-caudo-dorsad, and two lesser cornua 

 located at the junctions of the greater cornua with the body. 



