374 MANUAL OF ZOOLOGY sect. 



the fin are named, respectively, the anterior, pro-pterygium 

 (bs. i), the middle, meso-pterygium (bs. 2), and the pos- 

 terior, meta-pterygium (bs.j). Of these the first is the 

 smallest, and the last the largest. The pelvic fin has only a 

 single basal cartilage, articulating with the pelvic arch, with 

 which also one or two of the fin-rays articulate directly. The 

 pelvic arch is a nearly straight bar of cartilage which runs 

 transversely across the ventral surface of the body, just in 

 front of the cloacal opening. 



The mouth leads into a very wide cavity, the pharynx 

 (Fig. 216, ph), into which opens at the sides the internal 

 apertures of the branchial clefts and of the spiracle. From 

 this runs backwards a short wide tube, the (esophagus (gul), 

 which passes behind into the stomach. The stomach is 

 a U-shaped organ, with a long left limb (cd. st) continuous 

 with the oesophagus, and a short right (pyl. st) passing 

 into the intestine. At the pylorus — the point where the 

 stomach passes into the intestine — is a slight constriction 

 followed by a thickening. The intestine consists of two 

 parts, — small intestine or duodenum, and large intestine. 

 The former is very short, only an inch or two in length. 

 The latter (int) is longer and very wide ; it is divisible into 

 two portions, — the colon in front and the rectum behind. 

 The former is very wide and is characterised by the pres- 

 ence in its interior of a spiral valve, a fold of the mucous 

 membrane which runs spirally round its interior and both 

 retards the too rapid passage of the food, and affords a 

 more extensive surface for absorption. The rectum differs 

 from the colon in being narrower and in the absence of the 

 spiral valve ; it opens behind into the cloaca. 



There is a large liver (I. Ir, r. Ir) consisting of two elon- 

 gated lobes. A rounded sac, the gall-bladder, lies em- 

 bedded in the left lobe at its anterior end. The duct of 



