98 Proceedings of the Royal Physical Society. 



somewhat reniform, with one of the lobes produced and the 

 external margin straightened; the convex border is a little 

 flattened, angulated, and thickened, thence the bony fibres 

 radiate to the opposite or lobed margin. . . . The texture 

 of the bone is quite similar to that of the large triangular 

 carpal, namely, it is of a semicartilaginous appearance, with 

 coarse radiating fibres extending from margin to margin." ^ 



In other passages Messrs Hancock and Atthey clearly 

 indicate that they considered the thin margin, in both forms, 

 to be distal, and the apex, or point from which the " bony 

 fibres " radiate, to be proximal in original position. 



Before making any critical remarks on the above determi- 

 nation of the bones in question, it is necessary to fix accu- 

 rately to what elements of the Selachian skeleton Messrs 

 Hancock and Atthey compare them. 



The term " carpal " is not used by anatomists of the 

 modern school to denote any part of the skeleton of the fore 

 limb in fishes ; but on turning to Prof. Owen's " Compara- 

 tive Anatomy of the Vertebrata," vol. i., p. 168, Fig. 104, we 

 find the three basil cartilages of the pectoral fin of the picked 

 dogfish so designated. Two of these, the mesopterygiiim and 

 metapterygiiim of Gegenbaur, are triangular, with their apices 

 directed towards the shoulder-girdle, while the third or^?^o- 

 •pterygium has an oblong shape, faintly reminding us of the 

 second form of so-called carpal of Gyracanthiis. There can 

 thus be no doubt that these basal cartilages, which, in the 

 skeleton of the recent shark, intervene between the shoulder- 

 girdle and the radial cartilages, or cartilaginous fin-rays, are 

 the elements which Messrs Hancock and Atthey meant by 

 the term carpal. And the question is simply this, is it likely 

 that the process of calcification in such cartilages would give 

 rise to bodies like the peculiar bones so often found asso- 

 ciated with the spines of Gyracanthiis .? Or can any better 

 explanation of their nature be suggested ? 



One point in their external configuration was not noticed 

 by Messrs Hancock and Atthey, namely, that these bodies 

 were hollow, and that their extreme flatness is due to the 

 crushing together of the thin walls of the internal cavity. If 



1 Ann. & Mag. Nat. Hist., ser. 4, 1872, vol. ix., pp. 260, 261. 



