PULMONARY ARTERY. 607 



For preservative injections : — 



Beeswax 1 part. 



Tallow 3 parts, 



Vermilion, indigo, or Prussian blue, previously 

 mixed in oil of turpentine A sufficient quantity. 



Of course, it is well understood tliat these instructions are only intended for the dissecting- 

 room injections necessary for the study of descriptive anatomy. To inject the capillaries, it is 

 requisite to have recourse to other substances and other procedures. Suffice it to say that 

 these injections are made with cold fluids, such as varnish, alcohol, or spirits of turpentine, 

 holding ill suspension extremely fine colouring matter, gum arable dissolved and coloured by 

 a substance also in solution, etc., or, better still, colours rubbed up in oil, and mixed with oil 

 of turpentine. 



Dissection of the arteries. — There are no general rules to be given for the dissection of 

 arteries. 



CHAPTER II. 

 Pulmonary Artery (Fig, 349, e). 



Preparation. — The pulmonary artery is not filled by tlie general injection mentioned above. 

 It is directly injected by propelling the tallow into the right heart by the anterior vena cava, 

 after tying the posterior vena cava. 



The pulmonary artery arises from the infundibulum {conus arteriosus) in the 

 right ventricle, is directed upwards and then backwards, describing a curve the 

 concavity of which is infero-posterior ; on reaching the left auricle, it divides 

 into two secondary arteries — one for each lung. These arteries enter the pulmonary 

 tissue with the bronchi, and exclusively ramify in it. 



The pulmonary artery accompanies the trunk of the aorta on the right side, 

 and is enveloped with it in a serous sheath, a dependency of the visceral layer of 

 the pericardium. At its origin, it is flanked before and behind by the auric ules 

 and the cardiac vessels. About the middle of its course, it is united to the 

 posterior aorta by means of a yellow elastic fibrous cord (the ligamentum arte- 

 riosum), the remains of the ductus arteriosus which, in the foetus, establishes a 

 large communication between these two vessels (*Fig, 349, e). 



The w^alls of the pulmonary artery are much thinner than those of the aorta, 

 and are yellow and elastic, as in the other canals of the same order. We, how- 

 ever, have seen them in an Ass, formed almost entirely of red muscular fibres, 

 analogous to the fasciculi of the heart. 



It may be repeated that the pulmonary artery conveys to the lungs the dark 

 blood carried to the right heart by the veins of the general circulation. 



