ROOM III. BICONVEX CAUDAL VERTEBRA. 167 



vertebra in the adult Gavial is convex at both ends ; a remark- 

 able modification, required to connect the caudal series with 

 the sacrum, in consequence of the concavity of the posterior 

 articulation of the distal sacral vertebra ; this mechanism 

 confers freedom of motion without risk of dislocation. The 

 value of a knowledge of this fact to the palaeontologist was 

 quickly shown by the occurrence of a biconvex vertebra 

 among some Crocodilian bones from the Sewalik Hills, trans- 

 mitted to Dr. Buckland by Major Cautley and Dr. Falconer. 

 This bone had given rise to many vague conjectures before 

 the announcement of my discovery of this peculiarity in the 

 first caudal, which is the only vertebra of the series that pre- 

 sents such a structure, 1 and the only anterior caudal that has 

 no chevron-bone or hsemapophysis, (see Lign. 37). 



I must pass over other osteological characters, and proceed 

 to describe the interesting specimens which have called forth 

 these preliminary remarks. The student in comparative 

 anatomy, whose interest may be awakened by these brief com- 

 ments on the anatomical structure of the extinct types of 



1 On my return to Brighton, after a careful admeasurement of the 

 different parts of Dr. Grant's fine skeleton of a Gavial, in order to deter- 

 mine the generic relation of the Swanage Crocodile, I was surprised to 

 find that the double convexity of the first caudal was not mentioned in 

 the works of Cuvier, or in those of any other author to which I had 

 access; I therefore wrote to my kind friend, Dr. Robert Grant, and 

 requested him to examine the skeleton ; the following is an extract 

 from his reply : 



" You are quite correct. The first caudal vertebra of the Gavial, 

 the Crocodile, and the Alligator is, like the last cervical of Tortoises 

 and Turtles, convex at both ends of its body. It is not so in the Moni- 

 tors, nor I believe in the other families of Sauria, nor in the Chelonian 

 reptiles. 



" In a very young Gavial before me, these sacro-coccygeal surfaces are 

 as flat as in the vertebrae of quadrupeds, while in the Crocodile and 

 the Alligator at the same early period, the first coccygeal is as convex 

 anteriorly as you have observed it in the adult Gavial. The last sacral 

 is, of course, deeply concave posteriorly to receive the anterior ball of 

 the first caudal vertebra. I am not aware that you have been antici- 

 pated by any one in your observations on this part of the osteology of 

 the Gavial." 



" London, 15th March, 1836. " EGBERT E. GRANT." 



To place this fact on record as a guide to future investigators, I 

 sent a short description, with a sketch, to the " Lancet," which was 

 published in that Journal, June, 1836. 



The annexed figure, (Lign. 37,) represents, on a reduced scale, the 



