100 



and is connected by the anterior fold of integument to the cartilaginous peduncle of the orbit. 

 The maxillary arch is suspended by its palatal processes to the sides of the vomerine region 

 of the basis cranii : the tympanic pedicles are wanting. The occiput presents three facets for 

 the atlas, one on the basioccipital and two on the exoccipitals. 



Presented by Dr. Cantor. 



444. The dried head of a Hammer-headed Shark (Zygand). The teeth have an in- 



equilateral triangular crown, bent obliquely towards the angles of the mouth, 

 but sharp-pointed and with a finely serrated margin. Mits. Brit. 



445. A dried specimen of a young Saw-fish (Pristis antiquoruni). It shows the 



equal size of the large rostral teeth, and the very minute size of those of the 

 jaws. Hunterian. 



446. A dried specimen of a young Saw-fish (Pristis antiquoruni). Hunterian. 



447. The anterior extremity of the prolonged rostrum of a Saw-fish (Pristis), with 



three teeth in situ on the left side, and the sockets of the corresponding teeth 

 of the right side exposed. 



The teeth which are lodged in these sockets are elongated, compressed in the same plane 

 as that of the body of the saw, and the margins converge to a sharp point, which is 

 situated a little behind the 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, and the 

 groove glides upon a corresponding ridge which projects into the back part of the socket. 

 The rostral tooth is solid, as shown in the posterior one of the right side ; its base 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 formed by ossification of the rostral cartilage to the adequate ex- 

 tent ; but as undue weight under any circumstances, and especially at the fore end of the fish, 

 would be a cumbrous impediment to its motions, the spaces between the sockets are filled with 

 a gelatinous medulla. A large vascular canal, traversed by branches of the facial artery and 

 of the second division of the fifth pair of nerves, and inclosed in a cellular 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. 



Presented by Prof. Owen, F.R.S. 



448. The rostrum of a Saw-fish (Pristis antiquorum). Hunterian. 



449. The rostrum of a Saw-fish (Pristis antiquoruni). Hunterian. 



