m North America of rare Extinct Vertebrates. 209 



" thus the centra of the dorsals are hollow " *, I infer him 

 to mean that, in the recent state, the vertebral sinuses of his 

 reptile, like those in the pneumatic vertebrae of a bird, were 

 filled with air ; and he states that " they communicated with 

 the cavity of the body by a foramen on each side"t — meaning, 

 I presume, with such parts of that cavity as were continued 

 from the lungs and contained air. This, indeed, is placed 

 beyond doubt by the term " pneumatic " applied to the lateral 

 fossae in the dorsal and cervical centrums. On this assump- 

 tion he affirms, " the vertebrae are lighter in proportion to 

 their bulk than in any air-breathing animal," the cancelli 

 being relatively larger than in the vertebral centra of birds. 

 If, as I believe, the cancelli were occupied by unossified 

 gristle, or " chondrine," and supposing the deficiency of the 

 thin layer of bone at the bottom of the lateral fossee to be 

 natural, there would be no communication of the cancelli with 

 the cavity of the body or of any viscus therein lodged. The 

 vertebral centra would be solid, although constituted of two 

 tissues, as I conclude to have been the case with those of 

 PoikilopIeu7-on, in which the centrum is excavated by a large 

 central cavity or sinus (PI. X. fig. 5, ih), although there 

 are no lateral fossae \. On the other hand the lateral fossas 

 may exist without cancelli or sinuses in the substance of the 

 centrum, as e. g. in Bothriosjpondylus suffossus §. In Bothrio- 

 spondylus robustus \\ the cancelli are small, numerous, longi- 

 tudinally extended, ill-defined, wholly unlike the pneumatic 

 cancelli in the vertebrae of birds and Pterodactyles. But the 

 lateral fossae in extent and depth much resemble those in 

 Ckondrosteosawus, and retain their lining of thin compact 

 bone unbroken or imperforate. 



In Cetiosaurus longus ^ the lateral fossae coexist with a 

 closer osseous texture of the centrum than in Bothriospondy- 

 lus] the anterior trunk-vertebrae are opisthocoelian, as in 

 Chondrosteosaurus. The lateral depressions at the upper part 

 of the sides of the centrum occasion a '^singularly compressed 

 upper portion of such centrum underlying the neural canal 

 and forming a vertical medial plate of bone, three or four 

 inches in height and but six or eight lines in thickness " ** ; 

 but whatever parts in the thoraco-abdominal cavity may 



* Pal. Bull. 1877, p. 5. 

 t Proc. Amer. Phil. Soc. 1877, p. 233. 

 X Monog-r. 1876, pi. i. fig. 3, ch. 



§ Monograph on the genus Bothriospondylus in the volume of the 

 Palseontographical Society issued 1875, pp. 17-20, pis. iv. & v. 



II Ibid. p. 21, pi. vi. H Ibid. p. 29, pi. x. ** Ibid. p. 30. 



