16 CLASS XIV. 



In most fishes ribs {pleurapopTiyses Owen) are present : each rib 

 is attached to one vertebra alone, sometimes to its body, but 

 ordinarily to the extremity of the transverse process. These ribs do 

 not inclose the thoracic but the ventral cavity, and are not at- 

 tached to a sternum below. Only in very few fishes, as in the 

 herrings, the genus Clujjea, is there a sternum present, which, as it 

 consists of parts that belong to the dermal skeleton, might almost 

 be called external : to it the extremities of the ribs are attached. 

 Often, in addition to the ribs, there are little slender bones which 

 are attached to the ribs or to the vertebra? and lie amongst the 

 muscles. These fine spines are named the ossicles of Artedi {spines 

 e2n2ileurales Owen). 



The unpaired fins belong to the dermal skeleton and conse- 

 quently have no relation to the morphological survey of the vertebrse. 

 The caudal fin is usually attached to a triangular lamina which 

 consists of the body of the last caudal vertebra and a connexion of 

 the upper and lower spinous processes of some preceding vertebrae. 

 The rays of the dorsal and anal fins are attached by means of a 

 hinge-joint to small triangular flat bones, whose points are turned 

 towards the vertebral column, and which may be named interspinal 

 ossicles, since they lie between the spinous processes of the vertebrae. 

 Sometimes interspinal ossicles occur to which no rays are attached. 

 The first interspinal ossicle of the anal fin limits the ventral cavity 

 behind, and often unites with the inferior spinous processes of the 

 first caudal vertebra to form a firm part in form of an arch ^ 



The proper rays of the fins consist of two lateral parts, more or 

 less coalesced ; some are formed of joints and towards the extremity 

 split into branches. This applies equally to the rays of the ventral 

 and pectoral fins^. 



The pectoral fins are the anterior limbs of fishes, and correspond 

 to our arms or to the wings of birds. They are attached to an 

 osseous belt, which, in the bony fishes and sturgeons, descends 

 from the skull, in the sharks and rays from tlie spinal column, and 



^ In some species of Chidodon this bone is very thick, especially downwards. Here 

 belongs that singular bone which Olaus Woemius described, " quod siia figii^ra quasi 

 ■niurem rexira'sentat," Museum Wormianuni. Amstelodami, 1655, folio, p. 271. Com- 

 pare the figure of the skeleton of EiMppus giyas Cuv. in B. Wolf Diss, inaug. vied, 

 de Osse peculiarl Woj-mio dido. Berolini, 182 1, 4to. 



2 Compare on the spines of the fins Rosenthal in Reil's Archivf. die Physiol, x. 

 18 1 1, s. 359 — 372, with figs. 



