188 Sir P. G. Egerton on certain peculiarities in the 



stages of growth, some in their natural position in the skeleton, others de- 

 tached and rounded by attrition on the beach, all of which exhibited the same 

 peculiar features. Two views of a very perfect specimen, from the collection 

 of Lord Cole, which I have selected to illustrate the following details, are 

 given at plate XIV., figs. 1 and 2, 



Upon referring to fig. 2 it will be seen that the outlines of the two vertebrae are very clearly 

 defined ; I have found, however, by the examination of polished sections, that in the internal 

 structure the bony texture generally extends without interruption from one to the other*. 

 Once only have I succeeded, after the sacrifice of several specimens, in obtaining a forcible se- 

 paration of the two vertebrae, and in this case I found that no intervertebral cavity existed, the 

 bones articulating together by surfaces perfectly flat and even. (Fig. 3. A. B.) It is probable 

 then, that in individuals of tender years the atlas and axis existed as distinct bones, but the 

 extreme rarity of specimens in this condition, leads me to imagine, that the union between the 

 two, took place at a very early period of the animal's life. 



The atlas differs very materially from the other bones of the spinal column. 

 It is furnished anteriorly with a semicircular cup (Plate XIV. fig. 1. a.) for 

 the reception of the articulating tubercle of the basilar occipital, widely 

 different from the conical cavities of the other vertebrae; for whereas in these 

 the margin of each intervertebral cup is produced into a thin edge for arti- 

 culation with its neighbour, in the atlas it is rounded into the form of a thick 

 and solid lip, bounded on either side by a broad and rugged surface occupying 

 the position of the costal articulation, which probably served for the insertion 

 of the ligaments connected with the head. (Fig. 2. a.) 



The axis, as I have already remarked, is flat anteriorly for articulation with 

 the atlas. (Plate XIV. fig. 3. B.) It resembles the dorsal vertebras in the 

 form of the posterior cavity, as also in being furnished with bases for the 

 attachment of ribs. (Pigs. 2. d. and 3. c.) 



SUBVERTEBRAL WeDGE BoNES. 



I now arrive at a very remarkable feature, at once distinguishing the first 

 and second from the other bones of the spinal column, viz. the configuration 

 of the inferior part of the vertebral body. On the under surface of each 

 bone there exists an unusual enlargement in the form of a solid wedge-shaped 

 process placed transversely to the smaller diameter of the vertebrae. By this 

 arrangement four triangular planes are produced, disposed in the following 

 order. The first and largest (Plate XIV. figs. 1 and 2. b.), is based upon the 

 lower anterior margin of the atlantal socket, having its apex directed down- 

 wards and backwards until it meets the apex of a similarly shaped, though 



* See a polished slab in the British Museum from the collection of the late Mr. Bullock. 



