494* PISCES FISHES. 



The articulation between every fin-ray and the corresponding 

 interspinous bone forms a hinge-joint, so as to allow of the eleva- 

 tion or depression of the fin. The structure of this joint is very 

 beautiful, the two lateral halves of the ray separate so as to form 

 two branches, which firmly embrace the sides of the head of the 

 interspinous bone, and terminate in little prominent tubercles, 

 which are received into corresponding lateral depressions in the 

 bone to which the ray is attached. Sometimes, indeed, the head 

 of the interspinous bone is completely perforated, and then the two 

 branches of the fin-ray passing through the opening become firmly 

 united with each other, forming a kind of joint which is peculiar 

 to fishes, and exactly resembles the mode of union between two 

 links of a chain. This structure is beautifully exhibited in the 

 articulation of the elongated rays attached to the head of Lophius 

 piscatorius.* 



(530.) The composition of the skull of fishes is one of the 

 most difficult studies connected with their history ; nevertheless, 

 it is a subject of very considerable importance, and has recently 

 occupied the attention of the most celebrated Continental anato- 

 mists. It is not by any means our intention to engage our readers 

 in discussing all the conflicting and, sometimes, visionary opinions 

 entertained by different authors relative to the exact homology of 

 the individual bones forming this part of the skeleton ; and we 

 shall, therefore, content ourselves by placing before them, divested 

 as far as possible of superfluous argumentation, Cuvier's*!* masterly 

 analysis of the labours of the principal enquirers concerning this 

 intricate piece of anatomy, taking the Perch as a standard of com- 

 parison.^: 



The head of a fish may be conveniently divided, for the pur- 

 pose of description, into several distinct regions, each of which will 

 require separate notice. 



(531.) The Cranium, which forms the central portion of the 

 skull, contains the brain and auditory apparatus, and constitutes 

 the basis whereunto the other parts are connected. It is remark- 

 able from the number of distinct pieces of which it consists, inas- 

 much as in fishes the elements, or ossific centres, of which the 



* Vide YarrelPs History of British Fishes ; vol. i. p. 271. 8vo. 



t Cuvier et Valenciennes, Histoire des Poissons. 4to. vol. i. 



$ Those who would enter more fully into the discussions relative to the essential 

 composition of the skull, are referred to the works of Geoffroy St. Hilaire, Spix, 

 Rosenthal, Meckel, Bakker, Bojanus, and Oken, the great disputants upon this 

 subject. 



