88 HADROSAURUS. 
inferior teeth. At its connection with the crown it is pentahedral in section with 
the two outer sides corresponding with the sides of the carina of the latter. 
The measurements of the unworn upper tooth are as follows :— 
; Lines 
Length of the crown . : ‘ : ; , ; : : : : . 133 
Breadth at the lateral angles. s d : : ; 5 : : . 54 
Breadth at bottom. : 34 
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 . : 5 . woe 
Diameter of fang from within outwardly 4 
The specimens of inferior teeth appear to be nearly solid, that 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 which 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 into 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 was 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 crown exhibits a shield-shaped plane of dentine 
bounded in the upper teeth externally by a bow-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 XIII. In the upper jaw the slope of the dental pavement was directed down- 
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, 5. 
The intimate structure of the teeth of Hadrosaurus, 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 which 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 
