COMPOSITION OF THE SKULL IN FISHES. 631 



who hence derive the means of separating osseous fishes into two great 

 groups the Acanihopterygii, or such as possess spinous rays in the 

 composition of their dorsal fin, and the Mdlacopterygii, in which all the 

 fin-rays are soft. Every fin-ray, whether spinous or soft, is in reality 

 made up of two lateral halves placed side by side : in the soft rays these 

 are easily separable; but in the spinous rays they are firmly united 

 along the median line, so as to represent but one bone. 



(1696.) The articulation between every fin-ray and the corresponding 

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

 sponding lateral depressions in the bone to which the ray is attached. 

 Sometimes, indeed, the head of the interspinous bone is completely per- 

 forated, 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*. 



(1697.) The composition of the skull of Fishes is one of the most 

 difficult studies connected with their history ; nevertheless it is a sub- 

 ject of very considerable importance, and has recently occupied the 

 attention of the most celebrated Continental anatomists. 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 argu- 

 mentation, Cuvier'sf masterly analysis of the labours of the principal 

 inquirers concerning this intricate piece of anatomy, taking the Perch 

 as a standard of comparison J. 



(1698.) The head of a Fish may be conveniently divided, for the 

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

 require separate notice. 



(1699.) 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 remarkable from the 

 number of distinct pieces of which it consists, inasmuch as in Fishes 



* Vide Yarrell's History of British Fishes, vol. i. p. 271. 8vo. 



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



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

 composition of the sku'l are referred to the works of Geoffrey St.-Hilaire, Spix, 

 Rosentha!, Meckel, Bakker, Bojanus, and Oken, the great disputants upon this subject. 



