M E O A L O N Y X . 23 



arch, on a line with the posterior articular processes. They present on their outer 

 face a convex articular facet for junction with the tubercle of the rib; and at the 

 side of the spinal arch, below the position of the anterior articular processes, a 

 concave facet exists for junction with the head of the rib. 



The height of the posterior dorsal vertebra just described, from the postero- 

 inferior margin of its body to the extremity of the spinous process is nine inches ; 

 its breadth at the transverse processes is six and a half inches. 



Sacrum. — The fragment of a sacrum in the collection of Dr. Dickeson consists 

 of the upper part of the anterior three divisions of the bone ; and it is eight and a 

 half inches long. The spinal canal at the position of the first segment, is over 

 three inches in breadth, and it appeal's to have retained this size as far back as the 

 fragment extends. The spinous processes form a thick ridge, which is elevated 

 about an inch and a half above the surface of the spinal canal. The anterior 

 extremity of the fragment presents a broad process, formed by the conjunction of 

 the first sacral spinous process with the contiguous articular processes, appearing 

 to have served the purpose of a protection to the interval between the last lumbar 

 vertebra and sacrum. 



The last sacral vertebra (PI. VII, Fig. 5), in the collection of Dr. Owen, resem- 

 bles in its form the corresponding bone of MyJodon and the recent Ai. Its body is 

 transversely elliptical ; and at its anterior articular facet is slightly convex trans- 

 versely, and at its posterior facet in the same direction is slightly concave. The 

 breadth of the body anteriorly is three and a half inches, and its depth nearly two 

 inches. Posteriorly it is three and a quarter inches broad, by two and a half deep. 



The spinal canal is crescentic with rounded extremities ; and it measures three 

 inches in breadth by one and a quarter in depth. The spinous process is a short 

 thick ridge elevated about an inch above the surface of the spinal canal. The 

 anterior articular processes are prominent tuberosities projecting forward from the 

 spinal arch and supporting a small concave facet upon their inner side. The poste- 

 rior articular processes are slightly tuberous, and present their facet outward and 

 downward. The transverse processes are thick and strong, and project outward 

 and backward for four and a half inches from the body, and anteriorly they pre- 

 sent a long, oblique, rough surface for conjunction with the ischium. 



The height of the last sacral vertebra is four and a half inches ; its breadth is 

 ten and a half inches. 



Coccyx. — Of the two coccygeal vertebraB in the collection of Dr. Owen, one be- 

 longed to the anterior part of the tail, the other to the posterior part. 



The anterior vertebra (PL VII, Fig. 6), is broken into two. Its body is subcircular, 

 and is bounded by pentahedral articular faces, which are slightly convex. The 

 posterior face is continuous below with a pair of sloping facets for articulation with 

 a chevron bone. The breadth of the anterior surface of the body is three inches, 

 and its depth two and three-quarter inches. The spinal arch is broken away ; but 

 the canal between its abutments measures about an inch and a half in width. The 

 posterior articular processes are also broken away. Those anterior project obliquely 

 from the antero-superior angles of the body ; and they form a stout tuberosity, 

 supporting an ovoid articular facet upon their inner side. The transverse processes 



