DISSECTION OF THE VASCULAR SYSTEM. 5 1 



aftei' it is filled, and pushing tip the piston-i'-od until 

 the injection fiows from the end. 



To inject the veins it will be more convenie7it to in- 

 ject the superior cava and inferior cava separately, hi- 

 tr educe a cannula filled with the blue injcctioji into each, 

 and then force in the injection as in the arteries until 

 the veins are well filled. A sponge should be at ha7td 

 during the ivhole process to sop up any liquid or injec- 

 tion material zvhich may escape into the thoracic cavity. 

 By this process of injection the heart is not left in good 

 condition for dissecting, but this is supposed to have 

 beeit done before. 



The injectio7i of the arteries and veins can be made 

 also from the femoral artery and vein of one of the legs, 

 injecting in each case tozuard the heart and first wash- 

 ing out the blood with salt solution. This method, 

 however, is not so likely, in inexperienced hands at least, 

 to give good results. After injecting the animal must 

 be left some little time before using to allow the plaster 

 to set. 



A. THE DESCENDING AORTA. 



Find the aorta just beyond the arch, and dissect 

 toward the posterior. Turn the heart and lungs 

 toward the right, dissecting along the left side of the 

 thorax. If necessary cut off the ribs on this side nearer 

 to the vertebral column. 



1. The Intercostal Arteries come off from the aorta 

 in pairs in the spaces between the ribs ; they pass out- 

 ward alono^ the lower or posterior margins of the ribs. 

 The first intercostal from the aorta supplies the 5th 

 or sometimes the 4th rib, giving- a branch to the rib 

 above. The ist, 2d and 3d ribs are supplied by the 

 superior intercostal artery (see below). 



2. The Bronchial Arteries arise either from the 3d 



