654 DR JAMES STARK ON THE EXISTENCE OF AN OSSEOUS STRUCTURE 



41.55 per cent, of earthy matter, and in another 42.068 per cent, of earthy mat- 

 ter. These earthy matters consisted chiefly of phosphate of lime, with a small 

 proportion of carbonate of lime, sulphate of lime, muriate of soda, &c. 



It is evident from this analysis, that MULLER had not discovered the exist- 

 ence of the osseous structure which I describe, but had analysed the whole ver- 

 tebrae, laminae and all, considering it all to be what he terms ossified cartilage. 

 He had, in fact, made no distinction between the osseous nucleus and its en- 

 veloping cartilage, with its covering of calcareous granules. When I analysed the 

 vertebra in the same way, that is to say, with its cartilaginous laminse and envelop- 

 ing cartilages, I got, in one instance, in the Skate 53.3 per cent, of earthy matter, 

 and 46.7 of animal matter, and in the Thornback Ray 54.2 of earthy, and 45.8 

 of animal matters. But this gives no information as to the real amount of earthy 

 or animal matters in any part of the structure, seeing that the osseous base of 

 the vertebra contains a very different amount from the enveloping cartilage ; 

 and seeing, also, that the proportions will vary according to the relatively greater 

 or lesser size of the cartilaginous laminae and enveloping cartilage. 



The essential portion, then, of the vertebrae of cartilaginous fishes is true 

 bone, which has the same composition, and the same concentric laminar arrange- 

 ment, as the bones of osseous fishes. This fact appears to be of no small im- 

 portance in enabling us to arrive at more just conclusions regarding the position 

 which cartilaginous fishes ought to occupy in the scale of animated beings. 

 Possessing, as all the Plagiostomi do, in so far as their nervous, generative, and 

 digestive, systems are concerned, an organization superior to that of most fishes, 

 it always appeared an anomaly that they should, by their imperfect skeletons, 

 approach so much nearer the mollusca than other fishes. The discovery, how- 

 ever, of a perfect osseous structure in their vertebral column, that column 

 Avhich is the distinguishing mark of their belonging to the higher classes of ani- 

 mated beings, at once serves to explain the supposed anomaly, by shewing it 

 resulted from an imperfect knowledge of their true anatomical structure. 



In fact, the Plagiostomi ought to constitute a separate sub-class of fishes ; 

 and, in a descending scale of organization, be placed at the head of the fishes, as 

 they manifestly form the connecting link between the Fishes and Reptiles.* 

 While the Sturiones and Cydostomi ought to constitute another and distinct sub- 

 class, to which the term Cartilaginous might still be retained, and be placed after 

 the Osseous fishes in the descending scale of natural classification, forming, as they 

 undoubtedly do, the connecting link between the higher organised mollusca, and 

 the lower organised fishes. 



* Even the intervertebral ligamentary apparatus in the Plagiostomi makes a very close approach 

 to the same structure in the Amphibia. In many of the species, especially in those whose vertebral 

 cups are flat, it consists of concentric rings of fibro-cartilaginous matter, with softer albuminous or albu- 

 mino-cartilaginous matter between them. 



