48 REPORT— 1839. 



neurapopliyses and haemapophyses, but they are more rarely 

 aiichylosed at their central or proxmial extremities. 



The length which the ribs sometimes attain need form no ob- 

 jection to their being regarded as parts of a vertebra, when it is 

 remembered that the spinous processes, both above and below in 

 some fishes, are longer than the longest ribs in the same skeleton. 

 In the system of M. Geoffroy St. Hilaire, the nine elements of 

 a vertebra are completed by reckoning the spines of the dermal 

 skeleton, which in fishes are intercalated or articulated with 

 the neural and haemal spines of the true endo-skeleton as essen- 

 tial elements of a vertebra; and the paraaiix, or ha^majjophi/ses, 

 are described as being developed in length and changed in direc- 

 tion, in order to form the vertebral ribs of the thoracic and ab- 

 dominal regions. 



The vertebrae of the Bird and Ophidian already alluded to, 

 prove that vertebral ribs and inferior laminae or haemapophyses 

 may co-exist ; and the composition of the spine of the Plesio- 

 saurus, especially in the caudal region, well illustrates this fact : 

 for the costal appendages, which are generally anchylosed to the 

 other vertebral elements, in the cervical, sacral, and caudal re- 

 gions of the spine of the warm-blooded vertebrate classes, retain 

 their original separate condition throughout the vertebral column 

 in the Plesiosaur, and pass by such imperceptible gradations 

 from one condition of physiological subserviency to another, 

 that their nature cannot be mistaken when the entire series is 

 studied in a complete skeleton ; although, when seen in detached 

 vertebrae of the neck or tail, they present the appearance, and 

 have been generally described as, hatchet-bones, or transverse 

 processes. 



True transverse processes are, however, always exogenous, or 

 mere projections from the centrum or the neurapophyses, and 

 are of secondary importance. They are of tv/o kinds, superior 

 and inferior ; both are present in the cervical vertebrae in most 

 classes of the vertebrated animals ; the inferior transverse pro- 

 cesses alone are developed in fishes. 



The oblique, or articulating processes, are also exogenous, 

 and may be developed either from the neurapophyses, or the 

 base of the superior spines of the vertebrae. 



As in other complicated bones resulting from an association 

 of several osseous pieces, certain elements of a vertebra may be 

 modified in position and proportions, so as to perform the ordi- 

 nary functions of others M^hich may be atrophied or absent : 

 thus in fishes, the inferior transverse processes are gradually 

 bent downwards, until, in the dorsal region, their extremities 

 meet and perform the functions of the haemapophyses; 



