80 HADROSAURUS. 



twenty seven lines wide, and present no mark for the head of a rib. The latter, 

 however, apjjears to have been sitnated higher, exterior to the upper back part of 

 the position of the anterior articular processes, which are rather Avidcr apart than 

 those of the preceding vertebrae. 



No lumbar vertebrae or portions of a sacrum were discovered with the collection 

 of Hadrosaimis remains under examination. 



Eighteen caudal vertebrae, probably less than half of the original number, form 

 part of the collection. In all of them the body is moderately biconcave ; the con- 

 cavities being of nearly equal depth. The borders of the articular surfaces are 

 strongly everted, convex, and prolonged below into pairs of robust, sloping abut- 

 ments for the articulation of chevron bones. The . sides of the body are concave 

 longitudinally, convex vertically, and are defined below by obtuse ridges, extending 

 between the anterior and posterior chevron abutments. The under surface of the 

 body forms a concavity with a square outline whose angles are produced by the 

 abutments just mentioned. The articular ends are hcxahedral in outline. 



Three vertebrae, of which two are represented in Figs. 9, 10, Plate XIT, from the 

 commencement of the caudal series, are remarkable for their diminution in length 

 and great increase of breadth and depth, in comparison with the dorsal and cervical 

 vertebrae. Their body averages thirty-one lines in length, and in the three speci- 

 mens ranges from five inches and a half to six in breadth by about five inches and 

 a quarter in depth. They appear to haAO been provided with strong transverse 

 processes, as the broken roots of these extend from about the middle of the body 

 to the conjunction of the latter with the vertebral arch. The spinal foramen is 

 transversely oval, about nine lines in depth and fourteen in width. The breadth of 

 the abutments of the vertebral arch is about fifteen lines. 



The articular processes have subcircular flat facets, those in front being directed 

 obliquely towards each other, those behind looking obliquely outward and doA'sii- 

 ward. The anterior ones project a little in advance of the line of the front articular 

 surface of the body ; the posterior ones overhang the back articular surface. 



The ten succeeding specimens of caudal vertebrae, of which six are represented 

 in Figs. 11-16, Plate XII, exhibit a gradual but slight increase in length until 

 they almost equal in this respect the posterior dorsals above described, and they 

 undergo a gradual diminution in depth and width. The body of the eighth speci- 

 men in the series under consideration is about equal in bulk to that of the posterior 

 dorsals above described ; those in advance are larger, those behind are smaller. 



The first (Fig. 11) of the ten specimens has its body thirty-three lines long, sixty- 

 one broad, and fifty-four deep ; the sixth specimen has the body thirty-six lines long, 

 and fifty-one line's broad and deep; and the tenth (Fig. 16) has its body thirty-eight 

 lines long, and forty-three lines broad and deep. 



In succession, the abutments of the chevron bones become more distinctly defined 

 on each side by an intervening notch, wliich, however, at no time extends to their 

 base. 



The spinal foramen undergoes a gradual diminution in capacity and assumes a 

 more circular form. In the second specimen of the series it is nine lines deep and 

 twelve wide ; in the tenth it is eight lines deep and wide. 



