200 BRANCH CHORDATA 



Digestive System. — The food is principally animal. Food 

 securing is, of course, by the mouth. The mouths of fishes vary 

 in size, shape, and position, according to the food and feeding 

 habits. The digestive tract is large, near the region of the phar- 

 ynx, but narrows into a tube in which there is little distinction 



Fig. 159. — Right lateral view of skull of M. dolomieu, with other bones; 

 natural size: Pmx, premaxillary ; PL, palatine; na., nasal; Eth., ethmoid; 

 Prf., prefrontal; As., alisphenoid ; Fr., frontal; Ptf., postfrontal; Sq., 

 squamosal; Pa., parietal; Pt.o., pterotic; S.O., supra-occipital; si., supra- 

 linear; Ep.o., epiotic; k, interneural spines; La., lacrymal; Pr.s., para- 

 sphenoid; S.or., suborbital; Pr.o., prootic; Bs., basisphenoid ; G.Hy., 

 glossohyal; D,. dentary; Art., articular; Mx., maxillary; a, admaxillary; 

 Enpt., entopterygoid; EcpL, ectopterygoid; M.Pt., metapterygoid; 

 Pst.T., posttemporal; Pr..s., proscapula; Pf., pectoral fin; Hyo.C, hypo- 

 coracoid; Op., operculum; S.Op., suboperculum ; At^g., angular; Sym., 

 symplectic; tc.s., neural spine; Ps/o.T., post (Tot cm pnral; 7", telcotemporal; 

 T', lower telcotemporal; Bs.R., branchiostcgal rays; P.Op, preopcrcu- 

 lum; I. Op., interoperculum ; H.M., hyomandibular; Qu., quadrate; r., rib; 

 Ast., actinosts; Hyp.C, hypercoracoid. (Shufcldt.) 



between the parts. Many fishes have pyloric ceca at the junc- 

 tion of the stomach and intestine. Others have a spiral valve, 

 a fold of mucous membrane increasing the digestive surface. 

 There is a large liver and a spleen and usually a pancreas and 

 gall-bladder. 



