ARTERIES AND VEINS. 69 



constantly feels the degree of resistance ; for the pressure is 

 given directly by the fingers, instead of through a piston. 

 Another advantage is that the retort stand holds itself; and 

 if it becomes necessary to stop the pressure at any time, the 

 pinchcock may be applied to the tube, and both hands are 

 free for any needed adjustment, while everything is held in 

 readiness to go 011 with the work after simply loosening the 

 pinchcock. If a number of specimens are to be injected at 

 one time, a separate caimula may be used for each one, and 

 the lower end of the tube simply transferred from one to the 

 other. If desired, the mass may easily be stirred, or emptied 

 from the funnel. The cannula may be removed after ligatur- 

 ing the aorta, or a piece of rubber tubing slipped over the 

 cannula and tied. In any case, it is necessary to prevent reflow 

 of the mass until it hardens. 



The Distribution of the Arteries and Veins in the Cat 

 or Rabbit. (Injected.) 1. The main artery, the Aorta, is 

 a thick-walled tube, springing forward from the center of .the 

 base of the heart. It soon arches over to the left, and runs 

 along the middle .of the dorsal wall of the chest cavity. 



2. At the bend, or Arch, the aorta gives off two branches 

 (three in man). The first of these soon subdivides, giving off 

 a branch to the right f orelimb, the Right Subclavian artery ; two 

 branches running along the side of the windpipe are the Right 

 and Left Carotid arteries. The second branch of the aorta runs 

 to the left f orelimb, and is the Left Subclavian artery. 



3. During its course through the thorax the aorta is called 

 the Thoracic Aorta. Trace it to the point where it runs through 

 the diaphragm. It then becomes the Abdominal Aorta. Turn the 

 stomach and intestine over to the right, and observe the ab- 

 dominal aorta running along the dorsal wall of the abdomen. 

 Just posterior to the diaphragm, a branch is given off which 

 subdivides, and gives branches to the stomach, liver, and spleen. 



