HADROSAURUS. 89 
of the teeth, and is to be viewed as the remains of the pulp cavity. It is pervaded 
with vascular canals, the cut orifices of which may be seen in the section. 
The dentinal tubules pursue a gently undulating nearly parallel course, and the 
successive waves in the section, when viewed by transmitted light, appear alternately 
darker and lighter, giving rise to the impression of a concentric laminar arrange- 
ment of the dentinal structure. The tubules are exceedingly fine and arranged 
very closely together. They branch in their course outwardly and measure from 
the ;545,th to the 5545,th of an inch. 
The inner surface of the section (Fig. 1, a) is bordered by an enamel layer about 
the A,;th of an inch thick. The enamel folds around the lateral borders of the 
crown and ceases in a rather abrupt but thin edge. In the drawing, there is repre- 
sented a section (0) of a narrow isolated streak of enamel, which extended a short 
distance along the side of the crown. 
The outer border of the section (Fig. 1, d, Fig. 2, b) presents a peculiar layer, 
about jth of an inch thick, apparently consisting of a spongy reticulation of 
vascular tissue or vaso-dentine. It is this layer which gives the surface of the 
teeth, where not covered with enamel, a dull aspect; and it is friable and easily 
scraped off from the denser dentine within. ‘The vascular canals of the spongy 
tissue are of nearly uniform size and measure about the ;,!,,th of an inch in 
diameter. From the vaso-dentine many of the vascular canals penetrate into the 
denser dentine, in some cases to a greater depth than the whole thickness of the 
former, as represented in Fig. 2, Plate XX. 
The specimens of bones of the anterior extremity of Hadrosaurus consist of the 
humerus and those of the forearm of the left side. 
The humerus of Hadrosaurus, represented in Figs. 1, 2, 3, Plate XIV, bears a 
near resemblance in form and proportions to that of the /ywanodon as figured by 
Dr. Mantell' and Prof. Owen.” The upper part of the shaft is twice the breadth 
of its thickness, is concave transversely in front, and convex behind in the same 
direction, and has its inner border thinner than the outer. The lower part of the 
shaft is cylindroid, and gradually expands towards the condyles. 
The bone is broadest at its upper extremity from which the head projects pos- 
teriorly midway between two nearly equal tuberosities, which extend almost as 
high as the former. The head (a) is a hemispherical roughened prominence partly 
sustained by an abutment-like ridge extending downward on the back of the shaft. 
The upper part of the inner tuberosity (4) is convex and rough. The upper part 
of the outer tuberosity (c) is sigmoid aud likewise rough. 
From the inner tuberosity, the internal border of the shaft makes a continuous 
concave sweep to the lower end of the bone. From the outer tuberosity, the shaft 
remains expanded externally, to accommodate the attachment of the deltoid muscle, 
nearly to its middle (d), when the bone rapidly narrows to its lower cylindroid por- 
2 
2 Phil Trans. Roy. Soc., Lond., 1849, Plate XX Xi. Petrifactions and their Teachings, p. 286, 
Fig. 60. 
* British Fossil Reptiles, Dinosauria, Plate XIX, Figs. 3-6. 
12 April, 1865. Z 
