ANIMAL 
DENTITION. 
By R. LyDEKKER. 
il. FISHES. 
Parr I, 
Fig. 1. “Saw” of a Sawfish, with w portion cut away in order to 
show the mode of implantation of the teeth. 
1a the opening chapter of his great work on teeth the late Sir Richard Owen 
wrote as follows:—“If the ichthyologist have reason to complain of the monotony 
which unavoidably pervades his descriptions of the external characters of the objects 
of his study, the anatomist in treatine of the dental system of fishes, finds, on the 
contrary, his ditticulty in obtaining the command of language sufficiently varied to 
portray the simgular diversity and beauty, and the interesting physiological relations 
which are manifested in that part of their organisation. The teeth of fishes, in fact, 
in whatever relation they are considered, whether in regard to number, form, substance, 
structure, situation, or mode of attachment, offer more various and striking modifications 
than do those of any other class of animals.” 
This is by no means an exaggerated statement of the case, and when we take 
into consideration the vast number of kinds of fishes—recent and fossil—that are 
Inown to science, the difficulties which beset a writer who attempts to compress into 
the limits of a couple of articles even a few of the more important and interesting 
types of the dentition of fishes, can be better imagined than described. 
Not the least remarkable feature connected with the teeth of fishes is their 
variety of situation. They may occur, for instance, on all the bones or cartilages of 
the mouth, and are also frequently developed on the bones—the so-called pharyngeals— 
which strengthen the pharynx, or upper part of the throat. They may likewise be 
situated on the (hyoid) bones supporting the root of the tongue, as well as on the 
arches to which the gills are attached. Most remarkable of all is, however, the 
situation of the teeth of the Sawfishes, the largest of these beimg implanted in the 
well-known sword-like cartilage formed by a prolongation of the upper jaw, and thus 
being entirely outside the mouth. The “saw” is employed as a weapon of terrific 
power to tear open the bodies of whales and other marine creatures on which these 
gigantic and voracious fishes subsist. The teeth are fixed in distinct sockets on the two 
edges of the saw—a mode of implantation comparatively rare in the class. The teeth 
of the sawfishes are also remarkable from the circumstance that a single set has to 
serve throughout life, whereas in the great majority of the class the teeth of the 
jaws are constantly being shed and replaced by new ones. 
The position of the teeth of the sawfishes outside the mouth is, however, but a 
specialised reversion to a condition which probably obtaimed in the ancestors of all fishes, 
for it has been found that in their most prinutive condition the teeth of fishes correspond 
exactly in structure with the small bony and enamel-capped granules met with in the 
QB 
