184 



THE ELASMOBRANCPI FISHES 



sucliii, fig. 172a). In certain forms they may extend forward in a number of 

 strands {Cetorhinus, fig. 172b). The posterior cerebrals in Squalus (p.c, fig. 

 172a) loop around the inferior lobes of the brain and fuse into a single strand. 

 By the union of right and left posterior cerebrals behind and the anterior cere- 

 bral in front a circle of Willis is formed somewhat like that in man. Further- 



Fig. 173. Vascular supply to the digestive tract. A. TriaTcis semifasciatus, ventral view. 

 (Elizabeth Christiansen, orig.) B. Mustelus antarctieus, dorsal view. (From T. J. Parker.) 

 a.g., anterior gastric artery; a.g.v., anterior gastric vein; a.gps., anterior gastro-pancre- 

 aticosplenic artery; a.gs., anterior gastrosplenic artery; a.i.a., anterior intestinal artery; 

 a.i.v., anterior intestinal vein; ce., coeliac axis; co., colon; c.s., cardiac stomach; d.g., dorsal 

 gastric artery; d.i.a., dorsal intestinal artery; d.i.v., dorsal intestinal vein; gh., gastro- 

 hepatic artery; Ji., hepatic artery; h.'p., hepatic portal vein; i.a., intraintestinal artery; i.v., 

 intraintestinal vein; i.m., inferior mesenteric artery; Iv., cut end of liver; oe., oesophagus; 

 V-gs., posterior gastrosplenic artery; p.gs.v., posterior gastrosplenic vein; p.i.a., posterior 

 intestinal artery; pn., pancreatic artery; pn.^~^, dorsal and ventral lobes of pancreas; re, 

 rectum; spl., spleen; v.g., ventral gastric artery; v.g.v., ventral gastric vein. 



