50 DISSECTION OF THE VASCULAR SYSTEM. 



canting the excess, a7id finally mix the chr ornate held 

 in suspension in a little water with the plaster-of-Paris 

 solution. 



The injection of the vessels is best done as folloivs : 

 Dissect off the skill and mnscles fi^oui the ventral sur- 

 face of the thorax. Open the thorax by cutting 

 througJi the cartilaginous ribs at tJieir junction with 

 the bo7iy ribs on each side of the steimuni fro7n above 

 the diaphragm to the third rib, then cut transversely 

 across the stei-num and remove the piece of thorax 

 thus isolated. On the under side of the piece of the 

 sternum left at the anterior end of the thorax ru7i the 

 two sternal arteries and veins ; these must be Heated 

 either by dissecting thcTn out aiid tyiiig each separately, 

 or by passing a thread round the piece of sterniim 

 and bijiding firmly. 



Take a large cannula, to which a bit of rubber tub- 

 ing is attached, fill it with o.b^c solution of NaCl, 

 clamp the tubing, and then insert the cannula 

 into the aorta zvhere it springs from the heart and 

 ligature it firmly. Fill the syringe with the o. ti solution 

 of NaCl and inject it into the aorta, making mean- 

 while a cut in the right aui'icle throitgh which the blood 

 can escape. Continue the injection of NaCl solution 

 until all the blood is washed out. Then make the 

 yellow mixttire of plaster of Paris and inject it 7cntil 

 the arteries are tJioroiighly filled. If any escape takes 

 place from the small arteries C7it in opening the thorax, 

 these arteries can easily be ligated. In this as in all other 

 injections care must be taken not to let air get into 

 the vessel. The rubber tubing on the cannula should be 

 clamped each time the syringe is removed to be filled ; 

 ivhile in filling the syringe one must be careful alsa 

 to remove all air by holding it in an inverted position 



