

APPENDICULAR SKELETON. 



237 



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. 



Fig. 49. Scyllium canicula. The pelvic bar and fins of a male seen 

 from below. In the right fin the cartilaginous skeleton is shown, 

 hi the left the muscles and the horny dermal fibres, (a. m. m.) 



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

 skeleton of the clasper. 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 possibly 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 bar is a nearly straight rod of cartilage, 



placed transversely across the ventral region of 



the body, about half an inch in front of the 



