APPENDICULAR SKELETON. 



229 



often unite together, and the dorsal ends support 

 one or more rows of closely fitting polygonal plates. 

 On each side of this median cartilaginous skeleton 

 is a series of slender elongated horny fibres, derived 

 from the skin. 



The other median fins are similar to the dorsal 

 ones, except that the cartilaginous elements may be 

 reduced to a longitudinal basal rod, or may even be 

 completely absent. 



^M 



DF- 



FiG. 47. — Scyllium canicula. The pelvic girdle and fins of a male 

 seen from below. In the right fin the cartilaginous skeleton is 

 shown, in theleft the muscles and the horny dermal fibres, (a. m. m.) 



D, basi-pterygium. DC, posterior end of the basi-pterygium, forming tte 

 slceletou of the olasper. DF, radial cartilages. F, anterior radial, articulating 

 directly with the pelvic girdle. H, horny fibres. M, muscles. PG, pelvic 

 girdle. 



2. The paired fins are essentially similar to the median 

 fins, and are probably to be regarded as local enlarge- 

 ments of lateral fins, which originally extended 

 along the sides of the body. 



It is convenient to take the posterior or pelvic 



fins before the pectoral, as their structure is simpler. 



a. The pelvic girdle is a nearly straight bar of cartilage, 



placed transversely across the ventral region of 



the body, about half an inch in front of the 



