' FISHES. 13 



The fins are in part unpaired, situated in the plane that divides 

 the body into two lateral halves, in part paired, lying on each side. 

 The last may be four in number : two pectoral fins (pinnce pec- 

 torales), which are placed higher and behind the gills, and two 

 ventral fins (pinnce ventrales), which are situated more below. In 

 some fishes, as the haddock, these last are placed quite forward, in 

 front of the pectoral fins (pisces jugulares}', in others they lie almost 

 directly below the pectoral fins (pisces thoracici) ; but usually they 

 lie nearer to the tail, behind the pectoral fins, as in the carp (pisces 

 abdominales) . 



The unpaired fin at the end of the tail is called the caudal fin 

 (pinna caudalis), that which is attached to the body below, the 

 anal fin (pinna analis), that which is situated above upon the back, 

 the dorsal fin (pinna dorsalis). The dorsal and the caudal are 

 sometimes divided, or several separate fins are placed behind each 

 other. Adipose fin (pinna adiposa) is the name given to a small 

 dorsal fin without rays, which lies behind the ordinary dorsal fin, 

 as in the salmon. 



The small bones which support the fins, and between which the 

 skin of the fins is extended, are named rays (radii). These are 

 either composed of joints and often split at the point into different 

 filaments (radii molles), or simple, hard and pointed (aculei s. radii 

 spinosi}. When these last are present, they are situated at the fore 

 part of the dorsal and anal fin. The number of rays is used as a 

 specific character. Ordinarily the ventral fins are situated in front 

 of the anus, whilst the anal fin begins behind it. In some fishes 

 that have no ventral fins, the anus is placed far forward, close under 

 the head (the genus Sternarchus). 



This may suffice for the external form of fishes. We must now 

 consider their internal structure a little more closely, and to that 

 end shall first treat of their frame-work 1 . 



1 On the osteology of fishes, besides the general works on comparative anatomy by 

 CUVIER, MECKEL, &c., the following may be consulted: BOJANUS Versuch einer 

 Deutung der Knochen im Kopfe der Fische in OKEN'S Isis, 1818, I. s. 498 510; 

 GEOFFROY SAINT-HILAIRE Philosophic Anatomique, i. Paris, 1818, 8vo; G. BAKKER 

 Osteographia piscium. Groningse, 1822, 8vo (with folio plates, in which the parts of the 

 skeleton are principally illustrated in the haddock) ; L. AGASSIZ Recherches sur les 

 Poissons fossiles. Neuchatel, 1833 1843, 4to, I. pp. 91 152 (du Squelette desPoissons 

 en general) ; also in the work itself many osteological observations and -descriptions 

 of the skeleton of different genera are to be found, ex. gr. of Esox in the fifth part, 



