Vertebrae of Common Cod. 45 



the inverted suborbital arch^ and three or four others, the ossa 

 supratemporalia, occupy the space beneath the bifurcation of the 

 post-temporal scale, the so-called ' supra-scapula/ A black bristle 

 introduced into a canal passing- down the vertical limb of the 

 rectangular praeoperculum shows that it holds the same functional 

 relation to the muco-nervous ducts as the bones just mentioned. 



For accounts of experimental investigations into the functions of 

 the vertical and of the paired fins of fish, see Sir Anthony 

 Carlisle, Phil. Trans., 1 806, p. 4 ; J. Miiller, Vergleich. Ana- 

 tomic der Myxinoiden, 1845, p. ^^i Monoyer, Ann. Sci. Nat. 

 Ser. V. tom. vi., 1866. 



For the homologies and nomenclature of the shoulder girdle in 

 Fish, see W. K. Parker, on the Shoulder Girdle and Sternum 

 of the Vertebrata, pp. 4, 12, 50, 52, and fig. 6, D. p. 46. 



For the microscopic characters of the skeleton of osseous fishes, see 

 Kolliker, Royal Society^s Proceedings, 1859, is. p. 6^6. 



For those of the cartilaginous skeletons of this class, see Quekett, 

 Histological Catalogue, Coll. of Surgeons, ii. pp. 5-37. 



For those of the Chorda dorsalis, see Quekett 1. c. pp. 108, 109. 



13. Vertebrae of Common Cod {Gadus Morrlma). 



The anterior and posterior surfaces of the bodies of the vertebrae 

 are, as in the great majority of fishes, concave, and intercommu- 

 nicate with each other by a fine canal. These surfaces are marked 

 by concentric rings of striation, which are wider as we pass from 

 the centre of each terminal surface towards its periphery, and 

 indicate thus the rate at which the animaFs growth progressed. 

 Deep wedge-shaped cavities are observable around the periphery of 

 each vertebral centrum, two of especial depth and significance lying 

 in many vertebrae at the base of the parapophysial outgrowths on 

 their under surface, and bounding a single similarly shaped, but 

 sometimes shallower cavity in the middle line of that aspect of 

 each bone. The cod's vertebra resembles those of the majority 

 of osseous fish, but difiers from those of the common fiuviatile 

 representatives of the class such as the Cyprinidae, Salmonidae, 

 and Esocidae, in having its various processes and arches anchylosed 



