THE TELEOSTEI. 



137 



Most Teleostel possess two pair of limbs, the pectoral and 

 the ventral fins. But the latter are often absent, and the 

 former are occasionally wanting. When the pectoral fins are 

 absent, the pectoral arch usually remains, though it may be 

 reduced to little more than a filament, as in MiLrcenopMs, 

 The ventral fins are frequently situated in their normal posi- 

 tion beneath the posterior part of the trunk ; but in consider- 

 able groups of these fishes they are immediately behind the 

 pectoral fins {tlioracic)^ or even in front of them (jugular), 

 in the asymmetrical JPleuronectidcB one pectoral fin may be 

 larger than the other, or may alone remain, as in JSIonochlriis. 



The pectoral arch always consists of a primarily cartila- 

 ginous coraco-sccqjular portion — which usually ossifies in tAvo 

 pieces, a coracoid below, and a scapula above — and of sundry 

 membrane bones. The chief of these membrane bones is the 

 clavicula ( Gl.)^ which meets its fellow in the middle line, and 

 is usually joined to it by ligament, but sometimes, as in the 



ria, 49. — The bones of the pectoral arch and fore-limb of the Pike {Esov hiciiis): A, a 

 semi-diagrammatic view of these bones, to show their relative natural position. The 

 clavicle {CI) is supposed to be transparent. S.cl, supra-clavicula; p.cl, post-clavicula' 

 c, d, the posterior and anterior ends of the outer margin of the scapulo-coracoid. — B, the 

 scapulo-coracoid and hmb separate and on a larger scale ; Sep, scapula ; Ci\ coracoid ; 

 a, basal cartilages ; &, fin-rays ; c, corresponds with c in the foregoing figure. 



