FISHES. 275 



embraces the bones situated at the orifice of the pharynx, and which 

 constitute in some respect secondary jaws. 



The trunk is formed of dorsal and caudal vertebrae, (for we can 

 hardly speak of the existence of a neck, and it is quite certain that 

 there is no sacrum in fishes) of ribs, bones called interspinous, which 

 afford a support for the dorsal and anal fins, and to the rays of the fins, 

 as well as to those of the caudal. Such of the rays as have branches 

 and joints, or are simple spines, become divided into two equal portions 

 in the direction of their length. 



A sternum, properly so called, is very rarely found in fishes, and 

 when it does exist in a species, it is composed of two pieces which 

 are almost exterior, and on which the inferior extremities of the ribs 

 are united. 



The anterior limb, or the pectoral fin, consists of the shoulder, of a 

 bony half-girdle, composed of several bones, suspended at the top 

 of the cranium or spine, and uniting with each other beneath. 

 These bones are analogous to the two pieces of the scapula in reptiles, 

 to the humerus and bones of the fore arm. Generally, there is a 

 stylet of two pieces, in which the coracoid, and even the clavicle, may 

 be detected. But what is beyond all doubt is, that the two bones 

 which represent the ulna and radius, have on their edges a series of 

 very small bones, which appear to be the rudiments of those of the 

 Carp, and which do actually support the rays of the pectoral fin. 



The posterior limb, which varies a great deal more in its position 

 than in the mammalia, and the exterior and moveable portion of 

 which is called the ventral fin, is directed sometimes forward, at other 

 times downward, and also appears behind the anterior limb ; it is 

 composed of four bones, the largest of which, and they are the most 

 permanent likewise, being uniformly before the anus and orifices of 

 generation, may be regarded as a sort of pubis; they support on their 

 anterior edge, the rays of the fin without intermediate small bones, 

 which cannot be compared either to a femur, or tibia, a fibula, or even 

 to the bones of the tarsus. 



The rays of the pairs of fins are longitudinally divided into halves 

 as the vertical fins. 



After this general description of the parts into which the skeleton 

 is divided, we proceed to their individual examination. 



The Skeleton and the Head. 



The cranium of fishes is in general more distinct, it is more sepa- 

 rated from their face than that of any other of the vertebrated animals. 

 In a vast proportion of the species, the intermaxillary and maxillary 

 bones have a motion on the cranium by diarthrosis(a), and are inde- 

 pendent of each other in their motions, nay, independent even of the 



{J^» (a) This word means the sort of joint or articulation, in which two bones are 

 not joined or immovable, but which are kept contiguous by ligaments, and have 

 motion. — Eng. Ed. 



