180 



trituberculate talon and a cluster of very small mammillae behind it. 

 The coronal cement 611s up the bottom of the cavity between the last 

 transverse plate and the talon; the parallel transverse ridges and indenta- 

 tions of the base of the tooth are very strongly marked on the massive 

 posterior fang, especially at the parts where the cemental coat has been 

 removed; the summit of most of the transverse eminences is impressed 

 with a fine groove ; the apex of this fang is divided into three points, 

 the largest of which is curved. 



From the tertiary deposits of Ohio. Purchased. 



732. A portion of an inferior molar of the Mastodon gigantcus ; including the 



two posterior transverse ridges, and a narrow talon : each of the ridges 



is divided into two mammillae, each of which is again subdivided into 



two smaller ones. The ridges are united by a lower oblicpue ridge. 



From the tertiary deposits of Ohio. Mus. Parkinson. 



Stages of Growth of the Molar Teeth, 



733. A molar of a young Mastodon giganteus, the fourth of the left side, 



upper jaw, advanced in its formation to near the completion of the 

 crown ; the base, in which the indentations indicative of the three fangs 

 have just begun to appear, is a thin shell of dentine bounding a large and 

 widely open pulp-cavity. 



From the tertiary deposits of Ohio. Purchased. 



734. The corresponding molar of the right side of apparently the same jaw ; 



with one extremity vertically split off. 



From the tertiary deposits of the Ohio. Purchased. 



735. The extremity of the preceding tooth, showing the thickness of the 



enamel and the direction of the enamel fibres and dentinal tubes. 



Purchased. 



736. The crown of an incompletely formed molar of the Mastodon giganteus : 



the base is excavated by a large and single cavity, which contained the 



