IN THE VERTEBRAL COLUMN OF CARTILAGINOUS FISHES. (J51 



of bone and cartilage. These osseous plates are all beautifully cribriform, and, 

 by their numerous apertures, allow a free communication between the adjoining 

 layers of cartilage. The plates of bone, however, do not appear to send proces- 

 ses from one osseous plate to the other: each forms an in- Kg 10 

 dependent plate or layer encircling the layers within it. The 

 adjoining figure represents a section of this vertebra, A A re- 

 presenting the section of the two cup-shaped articular surfaces, 

 B B the concentric layers of osseous matter. The internal 

 layers are more condensed than the external ones. It ought 

 to be mentioned, that the osseous plates are partially interrupted on four sides. 



With this structure no additional means are required for giving support to 

 the vertebrae in violent motions of the animal, and none else are found present. 



In the Carcharias mdgaris, or White Shark, each vertebra is composed of two 

 very flat slightly hollowed discs, formed of concentric layers of osseous matter. 

 These discs are supported on four sides by very broad supports, which extend 

 from the outer margin to the centre of the discs. The lateral supports are by 

 much the broadest ; in fact, each supports about a third of the circumference of 

 the vertebral cups. These supporting columns are formed of plates of spongy 

 osseous matter, which extend from the circumference to the centre of the verte- 

 brae, and, in this respect, differ essentially from those of the Selache maximus, 

 which have a concentric arrangement. A central aperture perforating the body 

 of the vertebra is barely perceptible. 



In a young specimen of the Pristis antiquorum, or Saw-fish, an animal be- 

 longing to the same family as the Sharks, I found the internal portion of each 

 vertebra composed of a solid osseous portion, which, however, differed in its 

 specific characters from that of the other cartilaginous fishes. Each vertebra 

 was composed of two flat, but strong, somewhat rounded, cup-shaped bodies, so 

 flat, however, as to resemble two discs united by a narrow neck. In fact, the 

 vertebral column almost exactly resembled a continued series of the joints of some 

 of the Crinoidese. I could not detect any aperture piercing the body of the ver- 

 tebra, so as to allow the flat cup-shaped articular surface of the one side to com- 

 municate with that of the other. As the specimen was a young one, and had 

 but few of the vertebrae remaining, the rest having been removed for the purpose 

 of stuffing it, I am unable to give further particulars regarding them, or of the 

 mode by which they are strengthened ; but, from then* form, great strength, and 

 solidity, I do not think it likely that they receive Pig. n . 



any strengthening pillars. Figure 11 represents the 

 general form of the osseous portion of the vertebrae 

 of the Saw-fish viz., two rings or discs separated by 

 a neck, and hollowed into shallow cups on each articular surface. 



In the Chimcera, which belongs to a family closely allied to the Sharks, the 



VOL. XV. PART IV. 8 N 



