518 Richard OweNj Esq., on the 



of a vertebra in the abstract, has been generally adopted in this country. I was 

 compelled, however, to relinquish the advantage which the vertebral theory of 

 that philosophical anatomist seemed to promise, finding that it did not agree 

 with my observations either on the cartilaginous or osseous centres as they ap- 

 pear in the development of a vertebra in the embryo ; or on the fully-developed 

 elements as they are exhibited in different classes of the vertebrate series ; 

 more especially in certain parts of the vertebral column of the Plesiosaurus. 



I need hardly observe that a vertebra may be traced through its various de- 

 grees of complication, either in the progressive stages of growth of a complete 

 example, or by taking permanently-formed vertebrae in different animals ; or, 

 in many instances, by comparing them in different parts of the spine in the 

 same animal. 



The terminal vertebra; of the tail in most species exhibit the simplest con- 

 dition of these bones. The most complicated vertebrae which I have yet met 

 with are those at the lower part of the neck of a pelican (PI. XLIV., 

 fig. 3.) and some other birds, or the beginning of the tail of a python (PI. 

 XLIV., fig. 2.), or other large serpent. 



The parts or processes of such a vertebra may be divided into autogenous, 

 or those vi^hich are independently developed in separate cartilages, and exo- 

 genous, or those which shoot out as continuations from these independent 

 constituents: the latter are indicated by dotted lines in the diagram, fig. 1., 

 PI. XLIV. The autogenous, or true elements, are, 



1st. The centrum or body of the vertebra, which, in Mammalia, as Cuvier 

 has observed, is complicated by two epiphyses. 



2nd. Two superior laminae developed to protect the great nervous chord 

 which rests on the upper surface of the centrum, and which I have therefore 

 proposed to call neur apophyses*. In some Chondropterygians each centrum 

 supports four superior laminae. 



3rd. Two inferior laminae developed, generally to protect the great blood- 

 vessels on the under surface of the centrum, and which I have proposed to 

 call hcemapophysesf. 



* They are the periaux, or perivertebral elements of Geoffroy St. Hilaire. 



t These are the chevron bones of Mr. Conybeare, the paraaux, or paravertebral elements of 

 Geoffroy St. Hilaire ; — terms which he also apphes to the costal processes, — regarding these as the 

 expanded halves of the chevron bones. If I had adopted GeofFroy's terra, " paraal," or its English 

 equivalent, " paravertebral element," I must have diverted it from its original sense, in which it is 

 applicable to two distinct elements, viz. the ribs and chevron bones, which will be seen to co-exist 

 in certain vertebrae of the £na/ioxa!<ri, and some existing animals; and I have preferred, therefore, 

 to invent and define a new term, which has the advantage of expressing a physiological relation ; 

 and I am happy in being able to cite the authority of Cuvier for the propriety of this step. His 



