NEOCERATODUS 



B 



EUSTHENOPTERON 



Figure 6-60. Pectoral fins of choonote fishes as seen 

 Eusfhenopferon; C, Latimeria. 



\^ LATIMERIA 

 n dorsal view. A, Neocerofodus/ B, 



Actinopterygian fishes 



Pectoral appendage The pectoral girdle of the primitive 

 members of this array is essentially like that of the crossop- 

 terygian except that an interclavicle is usually lacking (Fig- 

 ure 6-63). There is generally a posttemporal, a supraclei- 

 thum, a postcleithruin, cleithrum, and clavicle. The clavi- 

 cle is present in Polypterus and Acipemer but lacking in other 

 living forms. An interclavicle is present in Aapenser (and 

 Scaphirhynchus but not Polyodon), where it lies dorsal to the 

 line between the clavicles (Figure 6-64). The clavicular 

 process of the scapulocoracoid cartilages meet above it. 



A postcleithrum is present in the primitive forms but 

 lacking in the teleosts generally. In Polypterus or Lepisosteus 

 the postcleithrum is associated with a line of scales along the 

 posterior margin of the girdle. In the salmon a thin post- 

 cleithral scale may be present and below this a second large 

 scale (as in Polypterus). Below this are one or two elongated 

 postpectorals lying in the fold of skin between the basal lobe 

 of the fin and the body (Figure 6-64). Two postpectorals are 

 generally present in teleosts, one above the other. The pxjst- 

 pectorals are new structures unique to the teleosts. 



The scapulocoracoid is cartilaginous in Amia and fairly 

 complex in form (Figure 6-64). That of Acipenser is similar 



but more massive and with a ventral process passing down 

 inside the ventral fin musculature. Also, the ventral muscles 

 which fan out the fin are separated by a cartilaginous pillar 

 from those drawing the fin toward the body. There is thus 

 an inner and outer ventral process. The salmon is like 

 Aapenser, except that it has only the inner of these ventral 

 processes; also it has three ossifications in the scapulocora- 

 coid: a (dorsolateral) scapula, which supports the radials of 

 the fin, a ( ventroanterior) coracoid, and a (dorsomedial) 

 mesocoracoid. The perch differs from the salmon in lacking 

 the mesopterygoid cartilage and bone. Polypterus is like the 

 perch in having only two ossifications but the coracoid lacks 

 any ventral process. 



The fins are supported by a number of radials. That of 

 the anterior (dorsal) margin of the fin is the largest and gen- 

 erally cartilaginous; it resembles a propterygium (Figure 

 6-66). The number of radials varies. In Anna and Aapenser 

 they are associated with a metapterygium. 



The fin of Polypterus is peculiar in that both pro- and 

 metapterygia are present. These are long rods separated by 

 a cartilaginous mesopterygium in which there is an oval 

 ossification. The radials lying distal to the mesopterygium 

 are more numerous than in the other fishes. There are two 

 series of radials, proximal and distal. This type of fin has a 



BILATERAL APPENDAGES 



181 



