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 presence
of the foreign body had continued to affect the normal development
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
which 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 requisite
for its subsistence ; but this seemingly imperfect armature of
the mouth is compensated for by the development from the anterior
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 ('Pristis antiquorum), from which the following description
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, fig. 9, b. (2) ib. fig. 9, a.
(3) In Pristis cirratus the apex of the small maxillary teeth is produced into a sharp point.
I and a series of deep alveoli is excavated in each of its lateral mar-
I gins-The teeth which are lodged in these 1 sockets are elongated, com- I pressed in the same plane as that of the body of the saw, and the mar- gins converge to a sharp point, which is situated a little behind the
II axis of the tooth ; the anterior border of the tooth is convex, but grows sharper towards the point; the posterior margin is concave or grooved,
I and the groove glides upon a corresponding ridge which projects into
1 the back part of the socket. The rostral tooth is solid, as shewn in
II the longitudinal section of the one figured in PI. 8, fig. 3 ; its base, I (fig. 5 ,) is slightly concave and porous, like the section of a cane, but the pores are finer and more numerous. The walls of the socket are
1 formed by ossification of the rostral cartilage to the adequate extent,
II [b. fig. 3) ; but as undue weight, under any circumstances, and espe- I cially at the fore end of the fish would be a cumbrous impediment to its motions, the intervening spaces {d. fig. 3) between the sockets
I3 are hollow and filled with a gelatinous medulla. A large vascular I canal (c. fig. 3) traversed by branches of the facial artery, and of the second division of the fifth pair of nerves, and inclosed in a cellular
I and gelatinous tissue, runs parallel with the axis of the saw along the back part of the alveoli, and supplies the materials for the increase
of the teeth, which are not shed and renewed like) the maxillary teeth,
but grow with the growth of the body by constant addition of fresh
pulp-material progressively ossified at their base.(l)
The structure of the rostral teeth of Pristis has the nearest resemblance
to that of the maxillary dental plates of Myliobates; they
are traversed throughout by medullary canals wdiich run parallel to
each other and to the axis of the tooth ; but they exhibit more frequent
anastomoses and dichotomous sub-divisions than in Myliobates.
The diameter of the medullary canals is y^th inch, and their interspaces
Ath of an inch near the base of the tooth ; they are surrounded
by concentric laminae which increase in number as the
(1) In the Pristis cuspidatus the rostral teeth are broad, and lancet-shaped ; in the Pristis
microdon they are very short; in the Pristis cirratus the rostral teeth vary in length, there being
from three to five smaller ones interposed between the longer teeth, which are sharp-pointed and
■ slightly recurved. The base of these teeth expands, and is excavated more deeply than in the
common saw-fish ; it is not socketed but anchylosed to the margin of the rostrum. The rostral