160 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 



horny fibres like those of the unpaired fins. (2) Pelvic fins 

 (Fig. 45). The two pelvic girdles are fused together into a 

 transverse bar of cartilage lying a little way in front of the 

 cloaca. Most of the bar (pubic region) lies between the attach- 

 ment of the free fins, but there is a small projection (iliac process) 

 external to this on each side. 



The inner side of the free limb is supported by an elongated 

 basipterygium ( = metapterygium) which in the male is continued 

 into the clasper. A series of fin-rays are attached to the outer 

 side of this cartilage, and one ray directly to the girdle. The fin 

 is completed by small plates of cartilage and by horny fibres. 



4. The digestive organs (Fig. 46) consist of the gut or 

 alimentary canal running from mouth to cloacal aperture, and 

 of appended glands. The sections of the gut are mouth-cavity, 

 pharynx, stomach, intestine, arid cloaca. The glands are the 

 liver and pancreas. 



The margins of the mouth are beset with several rows of 

 small, sharply-pointed teeth, which must be regarded as modified 

 placoid scales. The mouth-cavity is spacious, and upon its floor 

 there is an ill-developed tongue, supported by the basi-hyal 

 cartilage, and with a forwardly-directed rounded end. The 

 pharynx or respiratory section of the gut, which next succeeds, 

 communicates with the exterior by means of the spiracles and 

 gill-slits, and merges into a short, wide gullet (oesophagus) which 

 enters the abdominal cavity, and is there continuous with a large 

 U-shaped stomach. This is followed by the intestine, which 

 is divided into (a) a short, moderately-large bursa Entiana; (b) 

 a much larger and longer section, into which a shelf -like spiral 

 valve projects; and (c) a short narrow rectum opening into a 

 good-sized cloaca which also receives the excretory and genital 

 ducts. 



The liver is a large brown organ attached to the front end 

 of the abdominal cavity and divided into two long backwardly- 

 directed lobes. The secretion of the liver (bile) is carried away 

 by a bile-duct which opens into the middle section of the in- 

 testine, on the right side, not far from the beginning of the 

 spiral valve. A large gall-bladder connected with the duct is 

 imbedded in the left lobe of the liver near its origin. 



The pancreas is a small, pale, flattened gland situated in the 

 angle between the stomach and the bursa Entiana. The pan- 



