230 LABORATORY MANUAL FOR VERTEBRATE ANATOMY 



has shifted its anterior connections. Whereas in fishes it opens into the common cardinal 

 vein, in Amphibia it passes into the hepatic portal system. The abdominal vein thus becomes 

 a connection between the renal and hepatic portal systems and provides two outlets for the 

 blood from legs and tail. The pulmonary veins are new formations. 



D. THE CIRCULATORY SYSTEM OF THE TURTLE 



Specimens for the study of this system should have been doubly injected, 

 that is, into the arterial system, and in both directions into one ventral abdominal 

 vein. Remove the plastron. With the bone scissors cut away the sides of 

 the carapace between fore and hind limbs. 



i. The chambers of the heart. — The heart of the turtle possesses but three 

 different chambers, in contrast to the four chambers present in the forms already 

 considered; one of the chambers is divided into two completely separate halves. 

 Examine the heart in the pericardial cavity, removing the ventral wall of the 

 pericardial sac if this has not already been done. From the ventral view the 

 visible parts of the heart are the ventricle — the thick-walled, conical posterior 

 part — and the auricles — thin- walled chambers, one on each side anterior to the 

 ventricle. The two auricles are entirely separate from each other, as will be 

 seen later. The ventricle is attached to the posterior pericardial wall by a 

 ligament, which is apparently a remnant of the ventral mesentery or ventral 

 mesocardium of the heart, a structure which was considered in the general dis- 

 cussion of the coelom. Cut through this ligament, raise the ventricle, and press 

 it forward. A large chamber, the sinus venosus, is revealed dorsal to the auricles 

 and attached to the right auricle. The large bases of the systemic veins will be 

 seen entering the sinus. Put the ventricle back in place. Observe the large 

 vessels, arteries, which spring directly from the base of the ventricle without 

 the intervention of a conus arteriosus. The latter is lacking, or to be very 

 accurate, is so shortened down as to be invisible. The bases of the arteries which 

 spring from the ventricle correspond to the ventral aorta of elasmobranchs. The 

 ventral aorta is thus seen to have split into several separate trunks. The arteries 

 will be investigated later and should be left undisturbed at present. 



2. The ventral abdominal veins and the renal portal system. — Running in 

 the ventral pleuroperitoneum from the pelvic girdle up to the heart are two 

 large veins, the ventral abdominal veins. They are homologous with the lateral 

 abdominal veins of elasmobranchs. The two veins are generally connected just 

 anterior to the pelvic girdle by a cross-branch. Trace the veins forward. They 

 receive pericardial veins from the pericardial sac and then each turns dorsally 

 to enter the liver. Just at this turn each vein receives a pectoral branch from 

 the pectoral muscles of that side. Trace the pectoral vein into the muscle. 

 Slit the pleuroperitoneum alongside each abdominal vein and by lifting the cut 

 edges find the places where the vein of each side penetrates the lobe of the liver. 



Trace the ventral abdominal veins posteriorly. Make a longitudinal slit 

 in the pleuroperitoneum midway between the two veins, and separating the cut 



