BONES OF THE CHONDROPTERYGIANS. 59 



of small calcareous granules, which produce exter- 

 nally a stippled aspect. The form of the cranium is 

 similar to that of other fishes, but nevertheless con- 

 sists of only one enclosure, without sutures. The 

 face is very simple, with only two bones in the palato- 

 temporal arch : the first descending from the cra- 

 nium at the articulation of the jaws, the other 

 representing the upper jaw, and bearing teeth. The 

 maxillary and inter-maxillary bones are merely rudi- 

 mentary. The under jaw has also but one bone (the 

 articular) on each side, bearing the teeth ; of the 

 others only a single vestige is discoverable, concealed 

 beneath the lip. The opercular apparatus is wan- 

 ting, but the hyoidean and branchial structure is 

 very conformable with the same parts in osseous 

 fishes. Sharks have, moreover, opposite to the ex- 

 ternal attachment of each branchia, a slender bone, 

 which may be regarded as the genuine vestige of a 

 rib. The branchial system is situate further back 

 than in osseous fishes, and hence, the humeral girdle 

 just described, is also more posterior. The spinal 

 ribs, if they exist, are usually very small, except in 

 the sturgeons. In that genus indeed, the branchial 

 system is in some respects intermediate between 

 the cartilaginous and osseous fishes. Several bones 

 of the head and shoulder are as hard as stone, yet 

 the spine is almost as soft as that of lampreys, 



