PULMONARY ARTERY. 607 



For preservative injectione : — 



Beeswax 1 part. 



Tallow 3 parte. 



Vermilion, indigo, or Prussian blue, previously 



mixed in oil of turpentine A suflScient 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 tlie 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, suc-h as vaiiiisli, alcohol, or spirits of turpentine, 

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

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

 of turpentine. 



Dheection of the arteries. — There are no general roles 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, 

 •fter tying the posterior vena cava. 



The pulmonary artery arises from the infundibulum (conus arteriosits) 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 auricules 

 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 ligammtum arte- 

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

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



The walls 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. 



