50 M O S A S A TT R U S . 



The fossil teeth under examination would appear to indicate that the subdivision 

 of the inner and outj^r surfaces of tlie crown is best marked in the anterior teeth of 

 the series, becomes less evident in passing backward, and ceases in the last teeth. 

 Some of the specimens would appear to show that the subdivision of the cro\\ai 

 held some relation with the age of the animal; not existing in the young, but 

 developed in the mature animal. Other specimens appear to indicate that the 

 difference was due to individual peculiarity, or perhaps in some it may denote a 

 difference of species if not of genus. 



The fangs of the teeth of Mosasaurtis are remarkable for their great proportionate 

 size, being several times the bulk of the crown they support (Plate IX, Figs. 1-7; 

 Plate X, Figs. 1, 2, 4, 7, 8, 10). 



From the enamel border of the base of the crown the fang expands in the form 

 of a cone to the entrance of its socket, where it presents its greatest diameter and 

 is more or less defined by a shoulder or ledge (Plate IX, Figs. 1, 5; Plate X, Figs. 

 7, 8, 10; Plate XI, Figs. 1-6). 



The intra-alveolar portion of the fang, from two to four times the length of the 

 extra-alveolar portion, is straight, oblique, or slightly curved, cylindroid, and slightly 

 narrowed towards the obtusely rounded end. Frequently it is more or less com- 

 pressed from without inwardly ; and occasionally wrinkled at bottom. 



The mature fang was at first simply inserted about three-fourths or more of its 

 length in its socket, with which it was evidently adherent in the ordinary manner 

 by connective tissue. Subsequently, however, it became firmly coossified with the 

 alveolus ; the ledge or base of the extra-alveolar portion with the entrance of the 

 alveolus at the border of the jaw ; the intra-alveolar portion with the sides and 

 bottom of the alveolus. 



The pulp cavity (Plate IX, Fig. 6, /; Plate XX, Fig. 3, c) of the mature teeth 

 of Mosaf^aurus occupies a large extent of space in their interior. It is fusiform, or 

 doubly conical, one cone extending into the crown, the other into the fang. It 

 communicates by a large canal with a funnel-shaped pit, usually more or less com- 

 pressed, at the bottom of the fang.' Occasionally the canal is occupied by a coarse 

 cementum pervaded by many large vasculo-neural canals, as represented in the 

 diagram, Fig. 3, d, Plate XX. 



The crown of the teeth of Mosasaurus (Fig. 3, a, Plate XX) is composed of 

 compact dentine invested with a thin layer of enamel. At the base of the enamelled 

 crown the dentine extends, in the form of an in\^erted cone, within the extra-aheolar 

 portion of the fang and terminates in a thin, abrupt annular margin, encircling the 

 pulp cavity, as represented in the diagram, Fig. 3, e, Plate XX. 



The dentine, as represented in Figs. 4, 5, 6, a, Plate XX, presents the ordinary 

 constitution of an amorphous substance, pervaded with innumerable canaliculi 

 diverging from the pulp cavity to the periphery of the crown, dividing in their 

 course and giving off multitudes of lateral anastomosing branches. Below the 



' Owen says, "The pulp cavity generally remains open at the middle of the base of the crown of 

 the tooth; irregular processes of the cavity extend as medullary canals into the conical base of the 

 \ooth." Odoiitograi)liy, 259. 



