40 SHARKS. 



the posterior row of teeth, and had been broken off and fixed in 

 that position. (1) Now, had the growth of the jaw proceeded pari 

 passu with the movement of the teeth, the foreign body would in 

 time have been brought with the posterior row of teeth, to the outer 

 margin of the jaw, and have been discharged. If the shark had been 

 captured during this change, the teeth developed behind the wounded 

 row, might be expected to have been of the natural size and form ; 

 the appearances, however, presented by this interesting preparation 

 are as follows : a double row of imperfectly formed teeth is continued 

 from the perforated part of the jaw to the margin supporting the 

 erect teeth. (2) Hence it is obvious, that besides the original injury to 

 the formative pulps in existence at the time of the wound, the pre- 

 sence of the foreign body had continued to affect the normal deve- 

 lopment of the subsequently formed pulps. Thus it is proved that 

 the teeth and their supporting membrane advance forwards without 

 a corresponding movement of the particles of the cartilaginous jaw to 

 w^hich they are attached. 



14. Pristis. — The maxillary teeth of the saw-fish, which is an active 

 and predatory shark, are notwithstanding extremely small, simple, 

 obtuse, (3) and wholly inadequate to destroy and secure the prey requi- 

 site for its subsistence ; but this seemingly imperfect armature of 

 the mouth is compensated for by the development from the an- 

 terior part of the head of a very singular and formidable weapon, 

 provided with strong lateral teeth, and which, from its resemblance 

 to a saw, has given rise to the vernacular name of *' saw-fish," 

 applied to the present species of shark. 



In most of the plagiostomes but especially in the group of 

 squaloids, a conical projection or cutwater is continued from the 

 fore part of the head, and its frame work is composed of peculiar and 

 superadded cartilages, articulated to the anterior extremities of the 

 frontal, nasal and vomerine bones. These rostral cartilages (in the 

 common saw-fish f Pristis antiquorum) , from which the following des- 

 cription is taken) are blended into a horizontally flattened plate which 

 is produced to a length equalling one third that of the entire fish ; this 

 process is more completely ossified than any other part of the skeleton, 



(1) PI. 28, %. 9, b. (2) ib. %. 9, a. 



(3) In Pristis cirratus the apex of the small maxillarj' teeth is produced into a sharp point. 



