192 



SUB-CLASS (AND ORDER) TELEOSTEI, 



teeth (Ops). The hypobranchials, which may be wanting 

 in the fourth arch, are attached to a varying number of median 

 elements, the copulae or basibranchials (Cop). The fifth bran- 

 chial arch is reduced to a single rod on each side which is usually 

 strongly toothed, and the pair are called the inferior pharyngeal 

 bones (Opi) ; they are sometimes ankylosed to form a single 

 bone. The four anterior branchial arches bear small tooth-like 

 projections, in one or two rows, which act as strainers ; these are 

 the gill-rakers. 



Pectoral and pelvic* paired fins are present, but one or both of 



them may be absent. 



In the pectoral girdle, 

 which is usually present 

 even when the fin is 

 absent, the primitive 

 cartilaginous c o r a c o- 

 scapular elements are 

 but slightly developed 

 and relatively > unim- 

 portant, while the 

 membrane bones (clavi- 

 cles t) are largely de- 

 veloped. 



Flo. 112. Bight pectoral girdle and fin off Gadus 

 (after Gegenbaur). c clavicle (cleithrum) ; b 

 supraclavicle (supracleithrum) ; a post-temporal ; 

 d post-clavicle ; / scapula ; e coracoid ; g basal 

 somactids of the fin ; h bony dermotrichia. 



The coraco-scapular arches do not join ventrally and are 

 attached to the inner sides of the clavicles. They present two 

 bony elements the scapula and coracoid (by some regarded as 

 precoracoid) with persistent intervening cartilage. The scapula 

 usually has a foramen, and there is sometimes a third bony 

 element placed dorsal to the coracoid and in front of the scapula 

 and called the mesocoracoid. The clavicle (cleithrum) is a 

 large membrane bone meeting its fellow ventrally under the 

 throat. To its dorsal end there is usually attached a smaller 

 supraclavicle (supracleithrum) which is connected dorsally with 

 a forked bone the post-temporal. This bone is attached to the 

 auditory region of the skull, by one prong to the epiotic and 

 by the other to the pterotic bone. Projecting back from the 



* The pelvic paired fins are usually called ventrals. 



j- Called cleithra by some anatomists, on the view that they are not 

 homologous with the clavicles of higher Vertebrates (see notes, p. 162). 



