G4 REPORT— 1839. 



the neurapophyses, ns well as the canal for the spinal marrow, 

 are thus brought into view. The centrum presents only a plane 

 surface for the spinal cord, the rest of the canal being com- 

 pleted by the neurapophyses laterally, and the expanded base of 

 the spine above. The surface in question is bounded by two 

 lateral curved lines, having their convexities turned upwards to- 

 wards each other. Immediately below, and external to this 

 surface on each side, are the deep and roughened pits for the 

 attachment of the neurapophyses. 



The cervical neurapophyses do not in any of the Plesiosaurs 

 unite immediately together above the spinal cord and canal, so 

 as to form a continuous bony arch, spanning across that part ; 

 but they stand upright from their sockets in the vertebral body, 

 parallel with each other, or only slightly converging at their 

 superior extremities. They terminate above, in young indivi- 

 duals at least, in brqad rough articular surfaces parallel with 

 the transverse axis of the vertebrae, but sloping down from be- 

 hind forwards with a slight sigmoid flexure at an angle of 25° 

 with the longitudinal axis of the vertebra. 



In the same way, therefore, as the rib, or appendage to the 

 transverse processes, is bifurcate at its proximal extremity, in 

 those cases where the two transverse processes are separately 

 developed on each side of the vertebra, and where the rib is 

 joined to both ; so here the spinal appendage of the neurapo- 

 physes is bifurcate at its proximal extremity, and each fork 

 rests upon the above- described oblique articular process of its 

 own side. 



This analogy between the lateral or costal, and the superior 

 appendages of the vertebral centre, is one which the Plesiosau- 

 rtis alone has hitherto afforded. 



But besides the two surfaces developed for these articulations 

 with the neurapophysis, each fork of the spine sends off an ar- 

 ticular or oblique process from its anterior and posterior extre- 

 mity ; the articular surface looking obliquely upwards and in- 

 wards on the anterior process, and downwards and backwards 

 on the posterior process : and thus the spines are locked toge- 

 ther throughout the whole vertebral column with the exception 

 of the terminal vertebrae of the tail. 



In adult individuals of the PL macrocephalvs, these separate 

 elements of the superior arch become anchylosed together, as is 

 the case in a great part of the spine in the present specimen. 



In a Plesiosaurian cervical vertebra, however, measuring 

 seven inches and a half in vertical extent and three inches 

 and a half in transverse diameter, in the collection of Mr. Haw- 

 kins, I find the neurapophyses distinct both from the spine 



