I.] THE FROG. 89 



level of the vena cava inferior, and dissect away 

 the veins of the head. 



The dissection, as it now stands, presents a 

 general view of the blood-vascular system; 

 especially noticeable are the following. 



a. The renal portal system ( 4). The femoral and 

 sciatic veins will be seen to be united by an 

 anastomosing trunk, which encircles the outer 

 side of the thigh and receives veins from the 

 adjacent integument. 



b. The whole course of the vena cava inferior 

 (5)- 



c. The aortic arches ( 8). Examine these with 

 care; the middle one (aorta) may or may not 

 be connected with the other two, one or both 

 but most generally with the carotid arch, by a 

 longitudinal cord-like ductus Botalli. 



That portion of the ductus which connects the 

 aortic and pulmonary arches, and which is least 

 constant in the Frog, is also known as the ductus 

 arteriosus. 



ii. The anatomy of the heart. 



The examination of the heart requires a good 

 deal of care and the use of a lens of low magnifying 

 power, and it may be greatly facilitated by working 

 as follows. In a chloroformed Frog the heart is dis- 

 tended with blood when it ceases to beat. When all 

 signs of contractility have disappeared, the distended 

 heart should be removed from the body together 

 with the lungs and sufficient of the adjacent parts to 

 leave the terminations of the great veins and the 

 origins of the aortic trunks intact. The whole should 



