214 HUMAN ANATOMY. 



leolus, ascends the leg, and pierces the deep fascia in the popliteal 

 space, to terminate in the popliteal vein. The long saphenous 

 vein, and the larger, arises from the dorsum and inner side of the 

 foot, ascends the front and inner side of the leg and thigh, and 

 passes through the saphenous opening to join the femoral vein. 



THE PULMONARY VEINS. The pulmonary veins are four 

 short, venous trunks, two from the base of each lung passing 

 to the left auricle, returning arterial blood. 



They differ from other veins in the following respects : 



1. They are without valves; 



2. They carry arterial blood; 



3. They accompany the arteries singly; 



4. They are a little larger only than their arteries. 



The right are longer than the left, and pass from the root 

 of the lung, on a lower level than the artery, behind the aorta, 

 superior cava, and right auricle, to enter the left auricle. 



The Lymphatic System. 



The lymphatic system includes the lymphatic vessels and 

 glands and the lacteals, and forms an important accessory to the 

 blood-vascular system, collecting the transuded, unappropriated 

 fluids of the body and the nutritive material derived from the 

 food and conveying it into the venous system. 



It consists of two main trunks : 



(a) Thoracic duct; (It) Right lymphatic ductj 



and five smaller trunks : 



1. Jugular lymphatic trunk ; 



2. Subclavian lymphatic trunk; 



3. Broncho-mediastinal lymphatic trunk; 



4. Lumbar lymphatic trunk; 



5. Intestinal lymphatic trunk. 



Lymphatics have been found in nearly every organ and tex- 

 ture in the body except the brain, the spinal cord, cartilage, 

 tendon, eyeball, placenta, umbilical cord, membranes of the 

 ovum, hair, cutis, and the labyrinth of the ear. They appear to 

 originate as fine capillary nets interwoven among the blood- 

 vessels and proper elements of the tissues, or, more minutely, in 

 the lymph, perivascular, and perineural spaces. In the villi they 

 commence as closed, club-like tubes. 



The lymphatic capillaries are somewhat larger than the vas- 

 cular capillaries and destitute of valves. Their main trunks pass 

 through lymphatic glands lying in their course, before doing 



