duct is enclosed in a network of channels. Blood at first 

 flows from the caudal-subcardinal channel laterally to the 

 postcardinal channel. Later, when a caudal-renal portal 

 channel forms, the flow is reversed. 



Cydostomes 



LAMPREY The posterior cardinals of the lamprey arise from 

 the caudal vein, which in turn is formed from two lateral 

 caudal twigs from the lateral caudal hearts. These "hearts" 

 are contractile and communicate with the subdermal spaces 

 of the tail region. The posterior cardinals are joined by nu- 

 merous cross anastomoses along their length, and receive 

 various asymmetrical twigs from the gonads, kidneys, and 

 somatic regions (not from the digestive tract). The right 

 posterior cardinal is larger than the left. The left cardinal 

 joins the right just posterior to the level of the heart, and 

 both cardinals drain into the sinus venosus through the 

 right duct of Cuvier. 



The suprarenal sinus lies just below the cardinals through 

 out the entire length of the kidney. The sinus is connected by 

 narrow channels with the posterior cardinals. These open- 

 ings pass through a loose tissue lying along the ventrome- 

 dial wall of either postcardinal. Several venous channels 

 pass upward from the posterior end of the gut into the 

 suprarenal sinus. These are peculiar in that they enclose ar- 

 teries passing down to the gut. One of these arteries con- 

 nects with the intraintestinal artery of the typhlosole, while 

 the enclosing venous channel connects with the intrain- 

 testinal vein. Anteriorly the suprarenal connects with 

 the hepatic channels as well as with the right posterior 

 cardinal. 



Blood from the intestine (from the coeliacomesenteric 

 artery and posterior viscerals) is drained by a single mesen- 

 teric vein coursing along the right dorsal aspect of the gut. 

 At the anterior end of the intestine, the mesenteric vein 

 swings to the right and enters the substance of the liver, 

 which in the breeding adult has undergone fatty degenera- 

 tion with the loss of the gall bladder and bile duct. The 

 blood from the liver is picked up by a single median vein 

 which carries it to the sinus venosus. 



The intraintestinal vein is omitted in most descriptions. It 

 courses through the typhlosole of the gut, emerging to form 

 the anterior intestinal at the region where it leaves the gut 

 to enter the liver. Posteriorly the vein connects dorsally witli 

 the suprarenal sinus. 



In the early larva oi Lampetra the posterior cardinals (sub- 

 cardinal channels) enter paired ducts of Cuvier. The caudal 

 vein passes to either side of the anus to enter the subintes- 

 tinal drainage. The subintestinal vein connects antero- 

 laterally with bilateral vitelline stems to enter the heart 

 (Figure 11-42). The vitelline stems become the hepatic 

 veins; the left stem loses its connection with the subintestinal. 

 At this stage the gut begins to rotate counterclockwise, making 

 nearly one full turn so that the bile duct now extends from 

 the gall bladder to the left above the gut, and down around 



the left side to nearly the ventral midline where it enters the 

 gut. 



As this rotation takes place, the mesenteric artery is grow- 

 ing back along the course of the invaginating intestinal fold, 

 the typhlosole. The subintestinal vein has also been rotated to 

 a new position on the right aspect of the gut, draining directly 

 into the right posterior lobe of the liver. The caudal vein 

 now connects both with the posterior cardinal and the sub- 

 intestinal (mesenteric) channel. The mesenteric artery lies 

 in the midst of mass of myeloid tissue filling the typhlosole; 

 this myeloid tissue is the main embryonic site of blood-cell 

 production. Blood from this artery passes through the retic- 

 ulum of vessels enclosing the gut and enters the mesenteric 

 vein. 



_truncus arteriosus^ 



Figure 11-42. Development of intestinal drainage of the lamprey. 

 (After Goette, 1 900) 



CIRCULATION IN THE BODY 



375 



