14 CLASS 



The chief constituents of bony tissue are, as is well known, 

 phosphate of lime and gelatine. The organic constituent of the 

 cartilaginous bones in sharks is, according to CHEVKEUL, a peculiar 

 animal matter, which, in its chemical properties, has more resem- 

 blance to mucus than to gelatine. According to MUELLER, the gela- 

 tine from the bones of osseous fishes does not jelly. The cartilagi- 

 nous fishes have some parts of their skeleton which are more 

 ossified, and contain much phosphate of lime, as the bodies of the 

 vertebrae of sharks and rays, or they are coated with a hard ossified 

 layer 1 . The difference therefore between cartilaginous and bony 

 fishes is not very definite, since in these last moreover there is 

 much cartilage remaining, especially in the skull. 



We will now, first of all, confine ourselves to the form of the 

 skeleton. It consists of the trunk, the head, the bony or cartilagi- 

 nous apparatus of the respiratory organs and the fins. The spinal 

 column consists of dorsal and caudal vertebrae; for, since fishes 

 have no pelvis, there are no sacral nor lumbar vertebrae ; as little 

 are there cervical vertebras, for the cavity of the thorax is situated 

 under the head. Some writers indeed name those vertebrae that lie 

 nearest to the head and to which no ribs are attached, cervical ver- 

 tebrae ; but since there are many fishes that have no ribs at all, no 

 general use can be made of this distinction. 



The notochord [OwEN] (chorda dorsalis) is persistent in some 

 imperfectly organised fishes, and supplies the office of distinct bodies 

 of vertebrae. It is deserving of remark that this embryonal state 

 was very general in fishes of the earliest geological period, whence 

 the explanation is given that, in the remains of the so-named 

 Ganoids no bodies of vertebrae are met with 2 . In most of the 

 cartilaginous fishes, however, and in the bony fishes, bodies of 



pp. 60 68; Qwe,^ Lectures on the Comp. Anat. and Physiol. of the Vertebr. Anim. Pt. I. 

 Fishes. London, 1846, pp. 40 162. Here his theory of the cranial vertebrae is also 

 fully propounded. 



The richest collection of figures of the piscine skeleton is to be found in F. ROSEN- 

 THAL'S Ichthyotomische Tafeln. vi. Hefte. Berlin, 1812 1825. CUVIER, in the first 

 part of his Hist, natur. des Poissons, has figured and described the skeleton of Perca 

 fluviatilis in detail. 



1 Abhandlungen der physikalisck-mathematiscken Masse der Konigl. Alcademie der 

 Wissensch. zu Berlin. 1834, s. 136. 



3 AGASSIZ ascribed this previously to the accidental decomposition. Recherches 

 tiitr les Poissons fossiles, n. i, pp. 83, 84. 



