PISCES. 

 Fig. 495. 



96S 



'Skeleton of Lampris guttata, showing the interspinous bones, easily recognisable from their dark tint. 



are met with in acanthopterygious Fishes, and 

 branched or soft rays, such as are found in the 

 Malacopterygii. They are all divided by a 

 longitudinal raphe, or suture, into two lateral 

 halves, so that each appears to be formed of 

 two rays conjoined, a circumstance which 

 forms an additional argument against these 

 parts of the skeleton being dismemberments of 

 the vertebrae. 



The rays of the caudal fin are always soft 

 and articulated ; but in many Fishes some of 

 those at its root, both above and below, are 

 gradually diminished in size until nothing is 

 left of them but the hard part forming the base. 



Skeletons of Chondropterygii. In the true 

 cartilaginous Fishes, such as the Sharks and 

 Rays, the bones are always destitute of those 

 osseous fibres which give hardness to the skele- 

 ton in the preceding races possessing a true 

 bony skeleton. Their interior remains perma- 

 nently soft and cartilaginous, while their ex- 

 ternal surface is strengthened by becoming en- 

 crusted with a layer of granular-looking calca- 

 reous matter. 



As there is in the Chondropterygii no depo- 

 sition of bony particles radiating from ossific 

 centres, there can be no division of the cranium 

 into distinct bones, nor of course any sutures : 

 the whole cranium consists of a single cartilagi- 

 nous piece, in which, however, it is easy to dis- 



tinguish the same regions, the same fossse, the 

 same eminences, and the same holes as in the 

 skull of one of the osseous Fishes; but, although 

 it is not difficult with a little attention to point 

 out the situation of the different bones, to 

 define their limits is impossible. 



The bones of the face are likewise consoli- 

 dated with the great cranial mass, and conse- 

 quently are quite undistinguishable except from 

 their position in relation to organs into the 

 composition of which they enter. 



The structure of the skull therefore appears 

 exceedingly simple when compared with that 

 of an osseous fish. The whole pterygo-temporal 

 apparatus is represented by two pieces, one of 

 which corresponding with the temporal, tym- 

 panic, symplectic, and jugal bones of Cuvier, 

 or the tympanic pedicle, as Professor Owen 

 calls the long stem, which in the osseous 

 Fishes is composed of those elements, is here 

 represented by a single piece (jig. 496, c) in- 

 terposed between the side of the cranium and 

 the point of junction between the upper and 

 lower jaws an arrangement precisely similar 

 to that which is observable in the Batrachian 

 Reptiles. 



The other piece belonging to the pterygo- 

 temporal apparatus (fig. 496, e) forms, in con- 

 junction with its fellow of the opposite side, 

 almost the whole of the upper jaw, covering 



Fig. 496. 



Anterior portion of the skeleton of a female Shark ( Acanthias niaer). 



a, a, cartilaginous skull ; b, nasal cavity ; d, lower jaw ; e, upper jaw ; /, g, connecting pedicle ; 

 1, 2, 3, 4, 5, branchial apparatus ; 6, h, zone supporting (k, /,) pectoral fins. 



3 Q 2 



