PULMONARY ARTERY. 325 



which occurred during my dissections, the branches were the pro- 

 fund a, the superficial femoral, and internal circumflex artery. Dr. 

 Quain in his " Elements of Anatomy," records an instance of a high 

 division of the femoral artery, in which the two vessels became 

 again united in the popliteal region. The point of origin of the pro- 

 funda artery varies considerably in different subjects, being some- 

 times nearer to and sometimes farther from Poupart's ligament, but 

 more frequently the former. The branches of the popliteal artery 

 are very liable to variety in size ; and in all these cases the com- 

 pensating principle, so constant in the vascular system, is strikingly 

 manifested. When the anterior tibial is of small size, the peroneal 

 is large ; and, in place of dividing into two terminal branches at 

 the lower third of the leg, descends to the lower part of the inter- 

 osseous membrane, and emerges upon the front of the ankle, to 

 supply the dorsum of the foot : or the posterior tibial and plantar 

 arteries are large, and the external plantar is continued between the 

 heads of the first dorsal interosseous muscle, to be distributed to the 

 dorsal surface of the foot. Sometimes the posterior tibial artery is 

 small and thread-like; and the peroneal, after descending to the 

 ankle, curves inwards to the inner malleolus, and divides into the 

 two plantar arteries. If in this case the posterior tibial be suffi- 

 ciently large to reach the ankle, it inosculates with the peroneal 

 previously to its division. The internal plantar artery sometimes 

 takes the distribution of the external plantar, which is short and 

 diminutive, and the latter not unfrequently replaces a deficient dor- 

 salis pedis. 



The varieties of arteries are interesting in the practical applica- 

 tion of a knowledge of their principal forms to surgical operations ; 

 in their transcendental anatomy, as illustrating the normal distribu- 

 tion in animals ; or in many cases, as diverticula permitted by 

 Nature, to teach her observers two important principles -.first, in 

 respect to herself, that, however, in her means she may indulge in 

 change, the end is never overlooked, and a limb is as surely sup- 

 plied by a leash of arteries, various in their course, as by those 

 which we are pleased to consider normal in distribution ; and 

 secondly, with regard to us ; that we should ever be keenly alive to 

 what is passing beneath our observation, and ever ready in the 

 most serious operation to deviate from our course and avoid, or 

 give eyes to our knife, that it may see the concealed dangers 

 which it is our pride to be able to contend with and vanquish. 



PULMONARY ARTERY. 



The pulmonary artery arises from the left side of the base of the 

 right ventricle in front of the origin of the aorta, and ascends 

 obliquely to the under surface of the arch of the aorta, where it 

 divides into the right and left pulmonary arteries. In its course 

 upwards and backwards it inclines to the left side, crossing the 

 commencement of the aorta, and is connected to the under surface 



