958 



PISCES. 



Fishes. It is only less abundant, and conse- 

 quently the texture of the bone does not be- 

 come so hard or homogeneous. 



It is very gratuitously that the skeleton 

 of ordinary Fishes has been supposed to be 

 more flexible, of a softer nature, and more ex- 

 tensible than in the superior classes of Verte- 

 brata. Most Fishes have their bones as hard 

 as or harder than other animals, and there are 

 even some, in the texture of which neither 

 pores nor fibres are distinguishable, and which 

 appear homogeneous or even vitreous to the 

 eye. 



No Fish, either osseous or cartilaginous, has 

 a medullary canal in its bones ; but there are 

 some, as the Trouts, in which the bony tissue is 

 more or less penetrated with an oily fluid. 



There are some Fishes in which, whilst the 

 rest of the skeleton acquires great hardness, 

 some parts remain always cartilaginous, as for 

 example, the head of the Pike. 



SKELETON OF OSSEOUS FISHES. In osseous 

 Fishes, we shall regard the skeleton as being 

 composed of the head, of the respiratory appa- 

 ratus, of the trunk, comprising the body and 

 tail, and of the limbs, viz , the pectoral and 

 ventral fins. The vertical fins, viz, those of the 

 back, anus, and tail, may be regarded as form- 

 ing part of the trunk. 



The head having more moveable appendages 

 than that of Quadrupeds must be divided into a 

 greater number of regions. We may distinguish 

 in it the cranium, the jaws, the bones placed un- 

 der the cranium behind the jaws, serving for their 

 suspension and motions ; the opercular bones, 

 forming flappers, which open and shut the 

 openings of the branchiae ; the bones surround- 

 ing the nostril, which are nearly external, as 

 also are those around the eye or the temple, or 

 which cover a part of the cheek. 



The respiratory apparatus comprises the os 

 hyoides and its appendages, that is to say, the 

 branchiostegous rays and the arches supporting 

 the branchiae, as also the different pieces at- 

 tached to these arches, and which altogether 

 perform the functions of larynx and of trachea; 

 lastly, the bones placed at the entrance to the 

 pharynx, forming in some measure a second 

 pair of jaws. 



The trunk is composed of the vertebrae of the 

 back and tail (for we can hardly say there is a 

 neck, neither is there any sacrum,) of the ribs, 

 of the bones called interspinous, which support 

 the dorsal and anal fins ; also the rays of these 

 fins, as well as of the tail. These rays, whether 

 they have branches or articulations, or are 

 simply spinous, are always divisible into two 

 lateral halves. There is rarely a sternum, pro- 

 perly so called, in Fishes ; and when it exists, 

 it is formed of pieces which are almost external, 

 and which unite the lower extremities of the 

 ribs. 



The anterior extremity or pectoral fin com- 

 prehends the shoulder, which is an osseous 

 semicircle composed of many bones, suspended 

 at the upper part to the cranium or spine, and 

 uniting inferiorly with its fellow of the opposite 

 side. We may here find bones analogous to 

 the two pieces of the scapula of Reptiles, to 



the humerus and to the bones of the forearm ; 

 there is even generally a process composed of 

 two pieces protruding backwards, in which we 

 might seek to see the coracoid bones and even 

 the clavicle. 



The two bones comparable to the radius and 

 ulna carry at their edge a row of ossicula, 

 which appear to represent those of the carpus, 

 and which support the rays of the pectoral fin, 

 with the exception of the first, which articu- 

 lates at once with the radial bone. 



The posterior extremity is much more va- 

 riable in position than among Mammalia; its 

 external or moveable portion, called the ventral 

 Jin, emerges sometimes before, sometimes behind, 

 and sometimes immediately beneath the an- 

 terior extremity. The pelvis is composed of four 

 bones, the largest and most constant of which, 

 being always in front of the anus and genital 

 orifices, may be considered as a sort of pubis, 

 and these carry on a part of their posterior edge 

 the rays of the ventral fin, without interme- 

 diate bones which can correspond either to 

 femur, tibia, fibula, or tarsus. The rays of the 

 pectoral and ventral fins, as of those of the 

 single ones, are divisible longitudinally into 

 two portions. 



Vertebral column. The vertebrae of a Fish 

 are at once recognisable by the deep conical 

 cavities which form the articulating surfaces 

 whereby they are connected together, so that a 

 double hollow cone always occupies the in- 

 terval between two vertebra?, which in the 

 living state is filled up by a soft membranous 

 and gelatinous substance, which passes from 

 one intervertebral cavity into another through 

 holes which generally perforate the centres of 

 the bodies of the vertebrae. 



In Fishes, as in all other animals, each ver- 

 tebra presents superiorly a ring for the passage 

 of the spinal medulla bounded by the superior 

 spinal laminae (neurapophyses), which is gene- 

 rally surmounted by a long spinous process, 

 (fig- 493, 4,) at the base of which are situated 

 both upon the anterior and posterior aspect little 

 eminences that correspond to the articulating 

 processes of other Vertebrata; but most gene- 

 rally these processes only touch or slightly 

 overlap those of the neighbouring vertebrae 

 without their being connected together by 

 articulating facets. Sometimes, indeed, they 

 exist on one side of the vertebra and not 

 on the other, so that they have no corres- 

 pondents wherewith to articulate. The an- 

 nular part of the first vertebra is frequently 

 separated from the body during the whole life- 

 time of the Fish, but in the other vertebras no 

 such separation is visible. 



In some families, as in the Muranidte, part 

 of the anterior vertebrae have a little crest or 

 vertical apophysis developed from beneath the 

 body. Other races have a portion of the 

 bodies of their vertebrae soldered together; of 

 this there are examples among the Cyprinidae, 

 Fistularidae, and Siluridae. 



Those vertebrae which are situated above the 

 abdominal cavity have transverse processes de- 

 veloped to a greater or less extent. These, in 

 some instances, as, for example, in the Cy- 



