270 PETRIFACTIONS AND THEIR TEACHINGS. CHAP. III. 



of Jive as described in "Brit. Foss. Reptiles," p. 130), with the 

 right iliac bone attached. The relative size and proportions 

 of the several bones composing the sacral arch are now well 

 displayed. The body of the first or anterior vertebra is large, 

 strong, and expanded, forming a powerful buttress in front ; 

 the bodies of the two posterior vertebrae are likewise large 

 and strong ; but the second, third, and fourth, are constricted 

 laterally in the middle, and are more slender than either the 

 anterior or posterior ; by this modification of the elements of 

 the sacral arch, both lightness and strength were obtained. 1 

 A similar conformation is observable in every specimen of the 

 sacrum that has come under my observation, whether of young 

 and small, or of old and large individuals ; in all, the vertebrae 

 have the same relative proportions. 2 The only portion of the 

 sacrum of the Iguanodon in the British Museum, is the 

 detached vertebra placed above the tray containing the femur 

 marked No. 5, in the upper division of Wall -case C. (See 

 diagram, ante, p. 227. 2.) It evidently belonged to a young in- 

 dividual, for the body has separated from the contiguous bones 

 without fracture. 



THE PELVIS. ILIUM. Of the bones of the pelvis, namely 

 the Ilium, Ischium, and Pubis, specimens of the first only 

 have been found in connexion with the sacrum, or associated 

 with other parts of the skeleton. The right and left iliac 

 bones, detached from the pelvic arch, are imbedded near each 

 other, in the Maidstone fossil: and in Mr. Saull's, a con- 

 siderable portion of the right ilium remains attached in its 

 natural position. 3 Captain Lambart Brickenden has the 

 finest detached example of this element of the pelvis that has 



1 A detailed anatomical description of this sacrum is given in " Philos. 

 Trans." 1849, pp. 297299. 



2 Among the water-worn masses of bone strewn along those parts of 

 the southern shores of the Isle of Wight, which are bounded by cliffs of 

 the Wealden strata, I had often met with specimens in which the body 

 of a very large vertebra was anchylosed to one so disproportionately 

 small, that 1 could not explain their origin, until Professor Owen's 

 description of the structure of the sacrum suggested their true nature. 

 These fossils in fact consist of one of the large bones either of the ante- 

 rior or posterior end of the sacrum united to one of the slender middle 

 vertebrae. 



3 "Philos. Trans." 1849, PI. XXYI. A. 



