32 



cone to parastyle. A similar commissure occasionally extends pos- 

 teriorly behind base of metacone to metastyle, but this is less con- 

 stantly present. The paracone and metacone form the highest 

 portion of the tooth; the metacone, together with third and fourth 

 commissures, is usually larger than the anterior cusp and ridges. 

 A faintly developed cingulum may usually be traced along anterior, 

 inner, and posterior edges of crown. On outer side the cingulum is 

 practically absent. The third molar is always smaller than either of 

 the others, and some of its elements are reduced or absent. The 

 process of reduction, which invariably proceeds from behind forward, 

 varies, in teeth that can not be regarded as abnormal, from a mere 

 shortening of the metastyle and fourth commissure, accompanied 

 by diminution in height and diameter of the metacone, as seen in cer- 

 tain Rhinolophidse (Plate I, fig. 1), to absence of everything except 

 the parastyle, paracone, protocone, the first commissure, and a trace 

 of the second, elements which are always present in this tooth. This 

 condition is well illustrated by Pachyotus (Plate I, fig. 2). 



In the mandible the first and second molars are also alike in form, 

 with the second usually a little the larger. Five cusps are present, 

 the outer anterior protoconid (fig. 4, prcd.), the inner anterior para- 

 conid (fig. 4, pcd.), the inner median metaconid (fig. 4, mcd.), the 

 outer posterior hypoconid (fig. 4, hcd.), and the inner posterior 

 entoconid (fig. 4, ecd.). In general appearance these teeth resemble 

 the outer higher portion of the upper molars reversed, the three 

 inner cusps corresponding in form to the styles, and the protoconid 

 and hypoconid to the paracone and metacone. The hypoconid is, 

 however, lower than the protoconid, though the width of the tooth 

 through the base of this posterior cusp is normally greater than that 

 through the protoconid. The points of the cusps of the two rows 

 are nearer together than in the 'upper teeth, and the commissures 

 are shorter and more strongly concave, the third extending down- 

 ward from point of hypoconid to base of metaconid. The two seg- 

 ments of the W are therefore disconnected, though this is not at 

 first sight apparent when crowns are viewed from above. A well 

 developed though not very prominent cingulum extends around outer 

 base of crown from paraconid to entoconid. Third lower molar 

 with posterior segment usually much smaller than the first, owing 

 to the great reduction in size of both hypoconid and entoconid and 

 the close approximation of these two cusps. In some Rhinolophidse 

 and Emballonuridse, however, the tooth is practically identical with 

 to ! and m 2 (Plate II, fig. 1). In the first and second upper molars 

 of insectivorous bats the metacone may be said to be the dominant 

 cusp. It is not only the largest and the first to appear above 

 level of alveolus as the teeth grow, but in the modifications to 

 which the form of the crown is subjected the metacone invariably 



