284 BRITISH FOSSIL REPTILES. 



compared willi the sacrum of the Mcffahsaurus, which I had about tlie same time 



determined : 



" This instructive specimen consists of five vertebrae anchylosed together by the 

 articular surfaces of their bodies, and by their spinous processes, which seem to form 

 a continuous thick median ridge of bone. The articular extremity of the terminal sacral 

 vertebra is very slightly concave and subcircular, measuring 3 inches in both vertical 

 and transverse diameter. The bodies of the vertebrae are compressed at their middle 

 part, and broader below than in the dorsal region, and concave in the direction of their 

 a.xis, the concavities being separated by the broad prominent convex transverse ridges 

 formed by the anchylosed and ossified intervertebral spaces. The contour of the under 

 part of the sacrum thus forms an undulating line. The lateral and inferior surfaces are 

 separated by a more angular prominence of the centrum ; the under surface is less convex 

 transversely, and the whole centrum is shorter in proportion to its depth and breadth, 

 than in the Megalosanrus. The neurapophyses present the same remarkable modification 

 in reo-ard to their relations to the body of the vertebra as in the Mef/alosaurus, having 

 shifted their position from the upper surface of a single centrum to the interspace of 

 two, resting on proportions of these, which are more nearly equal, as the vertebras are 

 nearer the middle of the sacrum. The nerves were compelled, therefore, to escape 

 from the spinal canal over the body of the vertebra, more or less near its middle, and 

 impress the upper surface there with a smooth canal. The strong, vertically com- 

 pressed, transverse processes, or sacral ribs, rise from the bases of the neurapophyses, 

 and their origin extends upwards upon the spine, and downwards upon tlie sides of the 

 contiguous vertebral bodies and intervertebral space : in the specimen described they 

 are firmly anchylosed to all these parts, extend outwards, and expand to their 

 extremities, four of which meet, join, and form an elongated tract of varying breadth, 

 to which the ilium is firmly attached. 



" The length of the largest penultimate transverse process was 5 inches 8 lines, 

 its vertical breadth at the middle 3 inches, its thickness here 1 inch. The adjoining 

 (last) transverse process was 5 inches in length ; the interspaces of the transverse 

 processes equalled from 1\ to 2 inches. The sacrum increases in breadth posteriorly ; 

 its transverse diameter, including the anchylosed ilia taken at the posterior part of the 

 acetabulum, is 13 inches, at the anterior part of the sacrum only 8 inches.* The 

 proportion of the spine thus grasped, as it were, by the iliac bones, which transmit 

 the weight of the body upon the thigh-bones, corresponds with the mass which is to 

 be sustained and moved; and the size and structure of the sacrum indicate, with those 

 of the femur and tibia, the adaptation of the present great herbivorous Saurian for 

 terrestrial life," p. 130. 



I looked forward to the more detailed description, with illustrative figures, of this 

 unique specimen, when further worked out, as being likely to form one of the chief 

 * The true .interior limit of the sacrum is defined by this adnieasurenieut. 



