204 



ZOOLOGY 



SECT. 



PTG, 



\JJJ-.R 



Digestive Organs. The mouth (Figs. 865 and 876) is very 

 large and has numerous small, recurved, conical teeth, borne, as 

 already mentioned, on the premaxillse, maxillae, 

 palatines, vomer, dentaries and basihyal. 

 They obviously serve merely to prevent the 

 escape of the slippery animals used as food 

 and are of no use for either rending or chewing. 

 The pharynx (ph.) is perforated on each side 

 by four vertically elongated gill-slits, fringed 

 by the bony tooth-like gill-rakers. Each gill- 

 slit is V-shaped, the epihyal being bent upon 

 the ceratohyal so that the dorsal and ventral 

 moieties of the branchial arches touch one 

 another when the mouth is closed. 



The pharynx leads by a short gullet (gul.) 

 into a U-shaped stomach (st.) consisting of 

 a wide cardiac and a narrow pyloric division : 

 between the latter and the intestine is a ring- 

 shaped pyloric valve. The intestine passes at 

 first forwards as the duodenum (du.), then 

 becomes bent upon itself (int.) and passes 

 backwards, without convolution, to the anus 

 (an.). Its posterior portion has the mucous 



v ', , . * 



membrane raised into prominent annular 

 ridges which simulate a spiral valve. 



The liver (Ir.) is imperfectly divided into right and left lobes, and 

 there is a large gall-bladder (g. bL). Opening into the duodenum 

 are about forty blind glandular tubes, the pyloric cceca (py. c.). 

 There is a large spleen (spl.) attached by peritoneum to the fundus 

 of the stomach. The stomach, duodenum, and pyloric caeca are 

 surrounded by loose folds of peritoneum loaded with fat. 



Lying below the kidneys and extending the whole length of the 

 abdominal cavity is the air-bladder (a.bL), a thin- walled sac 

 serving as an organ of flotation. Anteriorly its ventral wall presents 

 a small aperture leading, by a short pneumatic duct (pn. d.), into the 

 oesophagus on the dorsal side somewhat to the right of the middle 

 line. 



Respiratory Organs. There are four pairs of gills each with 

 a double row of branchial filaments, united proximally but having 

 their distal ends free : interbranchial septa are practically obsolete 

 (see Fig. 780). The gills are borne on the first four branchial 

 arches, the fifth arch bearing no gill. On the inner surface of the 

 operculum is a comb-like body, the pseudo-branchia, formed of a 

 single row of branchial filaments, and representing the vestigial 

 gill (hemibranch) of the hyoid arch. 



Circulatory Organs. The heart (Fig. 876) consists of sinus 

 venosus, auricle (au.), and ventricle (v.). There is no conus arteriosus, 



B!' PTo r . sal basjptery- 

 glum; D.F.R. dermal 



fin-rays; PTG. distal 



pterygiophores. 



