V 



DIGESTIVE TRACT 



DIGESTIVE TRACT OP HEPTANCHUS MACULATUS 



Mesenterial Structures 



The digestive tract of HeptancJius (figs. 119 and 120) is suspended from the 

 dorsal body wall by mesenteries, which are present in two general areas, an 

 anterior and a posterior (fig. 120). The anterior mesenteries are somewhat 

 complex; while those which suspend the posterior part of the tract are simpler. 

 For couA^enience of description the mesentery in the anterior region may be 

 considered as made of a right, a median, and a left fold. The right fold of the 

 mesentery {r.f., fig. 120) passes from the middorsal line and from the right 

 suspensory ligament to the hepatic portal vein (h.p.) and to the spiral intes- 

 tine (sp.i), the extent of its origin, in other words, being along the middorsal 

 line from the liver in front, back to the region of the superior mesenteric ar- 

 tery. Since the anterior part of the right mesentery is attached along the 

 hepatic portal vein and back to the suspensory ligament of the spiral intestine, 

 it is largely hidden in figure 120. 



The second or median division extends from the right suspensory ligament 

 of the liver and the ligament along the hepatic portal vein, across to the 

 oesophagus and down the lesser curvature of the stomach to the proximal tip 

 of the duodenum. The larger part of this is shown in figure 120 (m.p.) with a 

 portion removed to show underlying organs. The left mesentery extends from 

 the middorsal line to the dorsal side of the oesophagus and the stomach. Along 

 its line of origin the left fold lies against the right and the two are firmly 

 fused together. Remnants of this part of the mesentery appear on the outer 

 angle of the stomach separating the stomach from the spleen (spl.) and from 

 the pancreas (pn.^). 



These three parts of the mesentery may be considered as loosely enveloping 

 the digestive tract and extending from the middorsal line on the right side to 

 the suspensory ligament and hepatic portal vein. From here the middle seg- 

 ment (omentum) stretches across to the lesser curvature of the stomach; the 

 left segment continuing around is attached to the middorsal line on the left. 



The posterior mesentery or mesorectum (mr.) extends from the middorsal 

 line to the rectal region ; it suspends the rectal or digitif orm gland, and reaches 

 forward to the posterior mesenteric artery. 



Buccal Cavity 



The mouth or entrance to the buccal cavity is ventral in Heptanchus. If seen 

 from below (fig. 119) it presents the appearance of a large crescentic slit with 

 regular margins, except near the angles where there are enlarged folds. The 



[121] 



