238 THE DOG-FISH. 



cloaca. The ends of the bar are produced for- 

 wards into blunt processes, and bear on their 

 posterior surfaces the articular facets for the 

 pelvic fins. 



b. The pelvic fins. The cartilaginous skeleton of each 



fin consists of a slightly curved basal rod, the 

 basi-pterygium, which lies along the inner side 

 of the fin, and articulates in front with the 

 pelvic girdle. From the outer side of the basi- 

 pterygium a series of parallel cartilaginous 

 radial cartilages, about fourteen in number, run 

 outwards and backwards, supporting at their 

 ends smaller polygonal plates. The anterior 

 one or two of the radials may articulate inde- 

 pendently with the pelvic girdle. 



In the adult male the posterior end of the 

 basi-pterygium is produced backwards into the 

 skeleton of the clasper. 



Besides the cartilaginous skeleton, horny 

 fibres like those of the median fins are present 

 in great numbers on both surfaces of the fin. 



c. The pectoral girdle, which lies immediately behind 



the last branchial arch, is considerably larger 

 than the pelvic, and consists of a hoop of carti- 

 lage incomplete above. 



The ventral portion of the hoop is produced 

 forwards into a flattened process, which forms 

 part of the floor of the pericardial cavity, and is 

 hollowed dorsally to receive the ventricle of the 

 heart. 



At each side the arch is thickened, and bears 

 on its outer border a triple articular facet for the 

 basal cartilages of the fin. 



d. The pectoral fin has three basal cartilages, the pro- 



pterygium, meso-pterygium, and meta-ptery- 

 gium, articulating with the three facets on the 

 pectoral girdle. Of these the pro -pterygium is 

 the smallest, and the meta-pterygium, which 



