350 MANUAL OF ELEMENTARY ZOOLOGi 



them in turn horny actinotrichia. The pelvic girdle is a 

 stout, straight bar of cartilage, placed athwart the belly and 

 bearing a blunt knob at each end. The main part of the 

 bar is the ischiopubic region, the knobs are the iliac processes, 

 and the fins articulate with an acetabular facet upon the 

 hinder border at the base of the iliac processes. The fin 

 has a long, inwardly-curved basipterygium, bearing a row of 

 radialia along its outer side. In the male it also bears a 

 long piece of cartilage which supports the clasper. 



The perivisceral cavity lies wholly in the trunk, and is 



divided into two parts, the small pericardium 

 coeiomand j us t; i n front of the pectoral fins, and the 

 system. large pleuro-peritoneal cavity behind it, between 



the two pairs of fins. The two cavities are 

 divided by a membranous septum, but a narrow passage, 

 the pericardio-peritoneal canal, leads from one to the 

 other below the oesophagus. As in the frog, the pleuro- 

 peritoneal cavity contains, among other organs, the whole 

 of the alimentary canal with the exception of the mouth 

 and pharynx. The gape of the mouth is edged with 

 several rows of teeth, which, as we have seen, are simply 

 enlarged scales. These lie in a part of the skin which 

 passes over the jaw and is tucked into a groove within it. 

 They are not in any way attached to the jaw. As they 

 wear away, they are replaced by new rows which are 

 constantly being formed in the groove and carried up over 

 the edge of the jaw by the growth of the skin. The 

 pharynx is only distinguished from the mouth by possessing 

 the inner openings of the spiracle and gill clefts. These 

 are placed between the arches of the visceral skeleton, the 

 first gill cleft lying between the hyoid and first branchial 

 arches. The clefts do not pass straight outwards through 

 the wall of the throat, but the outer opening of each is at 

 some distance behind the inner, so that the cleft is a pouch 

 which slants backwards and outwards from the pharynx to 

 the exterior. The pouches are spacious cavities, being 

 deep, and considerably taller than their openings at either 

 end, though the inner opening is larger than the outer. On 

 each wall of the pouch lie a number of folds which 

 constitute a gill. These are highly vascular, and in fresh 

 specimens have consequently a bright red colour.- There is 



