APPENDIX. 573 



It is evident that the pulmonary artery will not be reached by the 

 general injection already described. Inject it directly by passing the 

 injection into the right side of the heart, through the anterior vena cava, 

 after having tied the posterior vena cava. 



Dissection of Arteries. — There are no general rules to be given for 

 the dissection of arteries. 



Injection of Yeins. — It will make the study and dissection of the 

 veins easier, to fill them with injection ; but to do this, a difierent pro- 

 ceeding is followed from that described for arteries.- In place of making 

 the injection flow from the trunks towards the branches, as in arteries, 

 it must flow Jrom the branches to the trunks in the case of the veins, 

 owing to the presence of the valves. Four injections are in general 

 sufficient to fill the whole venous system in a satisfactory manner : the 

 first is poured through the alveolar vein under the masseter muscle; the 

 second into a digital vein of one or two fore-limbs, on the side of the 

 foot, after having destroyed with a stylette the several valves which are 

 sometimes found near the point of union of the roots of this vein, from 

 the cardiac side ; the third into a posterior digital vein ; the fourth into 

 an intestinal vein. If any important veins require to be studied after 

 these four operations, they are separately injected. 



THE LYMPHATIC SYSTEM. 



The lymphatic plexuses are studied after having being injected with 

 mercury, a proceeding which may be very briefly described, as it is 

 seldom done by those for whom this work is intended. The apparatus 

 commonly used consists of a tube of glass, continued by a flexible tube, 

 which carries at its lower end an iron stopcock and a fine cannula made 

 of iron or glass. To use this apparatus, fill the tube with mercury and 

 suspend it ; grasp the cannula with the right hand, holding it parallel to 

 the membrane which is to be injected, and push it into the superficial 

 layer of this membrane. The extremity of the cannula is thus intro- 

 duced into the middle of the meshes of the plexus, and of course wounds 

 one of the small vessels which compose it ; then turning the stopcock, 

 permit the mercury to flow into the vessels through the puncture. In 

 this way they may be perfectly filled. The lymphatic plexuses being 

 always placed above sanguineous ones, alv.rays take the precaution of 

 puncturing the membrane as superficially as possible, because if the 

 point of the cannula penetrate too deeply, the mercury passes into the 

 veins, and the operation is a failure. 



The study of the branches and trunks of the lymphatics may also be 

 facilitated by inflating them from their origin to their termination. If 



