XIII 



PHYLUM CHORDATA 



141 



the 

 only 

 ray 

 two 



r. 



respectively, the anterior, pro-ptcrygium (pro.), the middle, meso- 



pt&rygiurn (meso.), 



and the posterior, 



metapterygium 



(mcta). Of these 



the first is the 



smallest, and the 



last the largest : 

 first bears 

 one large 

 the other 

 bear twelve 



or more, diffe- 

 rently arranged in 



the two genera. 

 The pelvic fin 



(Fig. 771) has 



only a single basal 



cartilage (met a.) 



articulating with 



the pelvic arch, 



with which also 



one or two of the 



fin rays articu- 

 late directly. The 



pelvic arch (pelv.) is a nearly straight bar of cartilage which 



runs transversely across the ventral surface of the body, just 



in front of the cloacal 

 opening. 



Enteric canal (Fig. 772). 

 -The mouth leads into a 

 very wide cavity, the pharynx, 

 into which open at the sides 

 the internal apertures of the 

 branchial clefts and of the 

 spiracle. From this runs 

 backwards a short wide tube 

 -the oesophagus (ces) which 

 passes behind into the 

 stomach. The stomach is 

 a U-shaped organ, with a 

 long left limb continuous 

 with the oesophagus, and a 

 short right passing into 

 the intestine. At the 



pylorus (pyl) the point where the stomach passes into the 



intestine is a slight constriction, followed by a thickening. The 



FIG. 770. Chiloscy Ilium, pectoral arch and fin. d. r. dermal 

 horny rays ; meso. mesopterygium ; meta. metapterygium ; pect. 

 pectoral arch ; ^/-o. propterygium. 



FIG. 771.- 

 fiii. 



Chiloscyllium, pelvic arch and pelvic 

 ifta. metapterygium ; pelv. pelvic arch. 



