100 REPORT — 1839. 



parts as is requisite for swimming. In the separate state of the 

 neurapophyses in the Ichthyosaurs we perceive a condition 

 which is essentially Saurian, and one which doubtless would 

 add somewhat to the facility of inflecting the spine in the ver- 

 tical directions. 



The neurapophyses are interlocked together by means of co- 

 adapted oblique processes. The hsemapophyses are developed 

 beneath the abdominal and the caudal vertebrae ; they always 

 remain distinct from or unanchylosed to the vertebrae above, 

 and, so far as I have been able to form an opinion, are not 

 united together below, or to a common spine. 



With respect to the structure of the anterior part of the 

 cervical region of the vertebral column, different views may be 

 entertained. One theory is as follows : The atlas and axis 

 resemble each other and the succeeding vertebrae in size and 

 general form, as is the case in Fishes; but they are anchylosed 

 together, and the united surfaces are plain, presenting the only 

 deviation from the characteristic cupped structure recognisable 

 ill the rest of the vertebral column. Mr. Conybeare obsei*ves, 

 ^' We have only seen the inferior piece or body, if it can be so 

 called, of the atlas, and the odontoid process (which in all rep- 

 tiles forms a distinct piece) of the axis : they very nearly re- 

 semble those of the Turtle." It is not improbable that one or 

 other of the subvertebral wedge-bones discovered and well de- 

 scribed by Sir Philip Egerton may here be alluded to ; but Mr. 

 Conybeare afterwards believed that he had been deceived by a 

 mutilation of the occipital condyle. 



Comparative anatomists are not agreed as to the exact nature 

 or signification of the odontoid process ; its ossification always 

 begins by a distinct centre in the Mammalia, in which class it 

 becomes anchylosed with the body of the axis ; and it is gene- 

 rally regarded as a peculiar epiphysial appendage to the central 

 element of the 2nd cervical vertebra. According to this view, 

 the three subvertebral wedge- bones, which Sir P. Egerton has 

 so satisfactorily and perseveringly traced out, may be re- 

 garded as analogous epiphysial appendages of the first three 

 cervical vertebrae. Or they may be viewed, with the odontoid 

 process, as haemapophyses or inferior appendages of the verte- 

 bral centres in a rudimental state ; and the vertebral cup which 

 receives the occipital tubercle may be deemed, as in fishes, to 

 be formed by the atlas. 



On the other hand, if we look to the Saurians for a clue to 

 the homologies of the structure in question, we find that the 

 body of the atlas in both the Crocodilian and Chelonian Rep- 

 tiles is always remarkably small, and the greater part of the 

 articular concavity which is adapted to the occipital tubercle is 



