88 IIADROSAURUS. 



inferior teeth. At its connection with the crown it is pentahedral in section with 

 the two outer sides corresponding with tlie sides of the carina of the hatter. 

 The measurements of the unworn upper tooth are as follows : — 



Lines. 



Length of the crown . 13^ 



Breadth at the lateral angles .......... 5^ 



Breadth at bottom ............ 3^ 



Greatest diameter from within outwardly or from the prominence of the bottom 

 of the crown internally to the edge of the carina externally .... 8 



Diameter of fang at its connection with the crown transversely .... 3^ 



Diameter of fang from within outwardly ........ 4 



The specimens of inferior teeth appear to be nearly solid, th^t is to say, their 

 pulp cavity is almost obliterated, as a portion remains pervious only for a short dis- 

 tance within the fangs. In one of the specimens, in wliich the fang is broken off 

 near its conjunction with the crown, the remains of the pulp cavity form a linear 

 suture extending through the middle half of the diameter from within outwardly. 

 The sides of the pulp cavity, where visible, are exceedingly rough and pitted, the 

 pits corresponding with a multitude of minute offsets diverging from the main 

 cavity hi to the dentine. 



As the teeth of Hadrosaurus were worn away from attrition to which they were 

 subjected, a flat, or very feebly depressed, oblique triturating surface Avas produced 

 and gradually increased in breadth to the middle of the crown, and then as gradually 

 decreased to the fang, upon which it was also continued until this became worn 

 out. The triturating surface of the croAvn exhibits a shield-shaped plane of dentine 

 bounded in the upper teeth externally by a boAV-like border of enamel ; in the lower 

 teeth bounded in the same manner internally. 



The series of teeth at the border of the jaw in functional position appear to have 

 formed a continuous sloping pavement, presenting triturating points and facets of 

 different sizes and of several patterns, according to the portions of the teeth which 

 had reached the triturating surface, as represented in the partially ideal Fig. 18, 

 Plate XIIT. In the upper jaw the slope of the dental pavement was directed doAvn- 

 ward and inward, and was margined externally by a festooned cutting edge of 

 enamel, as seen in Fig. 18, d. In the lower jaw the arrangement was reversed, 

 the dental pavement being parallel with the former and slanting with a direction 

 outward and upward, and the festooned cutting edge of enamel being internal, as 

 seen in Fig. 19, a, h. 



The intimate structure of the teeth of Hadrosawus, as viewed by the microscope, 

 is exhibited in Fig. 1, Plate XX, representing the transverse section of the crown 

 of an inferior tooth above its middle. The representation is not to be viewed as 

 exact, as the proportions of the whole section and the elements of structure, for 

 obvious reasons, have not been preserved. It is rather a diagram exhibiting the 

 relative position of the structural elements in the transverse section of the crown 

 of a tooth. 



The section is mainly composed of hard dentine in wliich the dentinal tubules 

 emanate from a median crucial line and radiate towards the periphery. The crucial 

 line corresponds with that previously mentioned as visible on the triturating surface 



