THE VEINS; — PULMONAEY VEINS — CARDIAC VEINS 681 



descends in the furrow between the medial small and large metatarsal bones, and 

 anastomoses usually in the proximal part of the metatarsus with the medial super- 

 ficial plantar metatarsal, uniting sometimes with the medial deep plantar meta- 

 tarsal. The lateral vessel passes do^vn under the periosteum on the dorsal face of 

 the large metatarsal bone and becomes lost or joins the great metatarsal artery. 



In rare cases the anterior tibial artery passes undi\-ided through the tarsus, gives off the 

 medial deep plantar rnetatarsal, and is continued as a \ny large medial superficial plantar meta- 

 tarsal along the deep flexor tendon, thus resembling the arrangement in the foreUmb 



^ In a few cases the perforating tarsal is a large vessel, directly continuing the anterior tibial 

 and IS continued by a large medi'al deep plantar metatarsal. The great metatarsal is then small! 

 Utner variations are common. 



THE GREAT METATARSAL ARTERY 



This artery (A. metatarsea dorsalis lateralis) is the direct continuation of the 

 anterior tibial. It descends, inclining outward, under cover of the extensor brevis 

 and the tendon of the lateral extensor, at first on the joint capsule and then in the 

 oblique vascular groove on the proximal part of the large metatarsal bone. It then 

 descends superficially in the groove formed by the apposition of the large and lateral 

 small metatarsal bones, passes between the two, and divides on the distal part of 

 the plantar surface of the large metatarsal bone into the medial and lateral digital 

 arteries. It is not usually accompanied by a vein. It is joined near its termination 

 by two or more of the plantar arteries, and beyond this the term common digital 

 artery (A. digitalis communis) may be applied to it. In the digital region the 

 arterial arrangement is the same as in the thoracic limb; it is only necessary in 

 reading the description to substitute the word "plantar" for "volar." 



THE VEINS 1 



PULMONARY VEINS 



The pulmonary veins (Vv. pulmonales), usuall}' seven or eight in number, 

 return the aerated blood from the lungs and open into the left atrium of the heart. 

 They are destitute of valves. Their tributajries arise in the capillary plexuses in 

 the lobules of the lungs, and unite to form larger and larger trunks which accompany 

 the branches of the bronchi and pulmonary arteries. A very large vein is formed 

 by the union at an acute angle of a trunk from each lung, where the latter are ad- 

 herent to each other. 



CARDIAC VEINS 



The coronary sinus (Sinus coronarius) is a very short, bulbous trunk which 

 receives most of the blood from the wall of the heart. It is situated just below the 

 termination of the posterior vena cava, and is covered in part by a thin layer of 

 atrial muscle fibers. It opens into the right atrium just below the posterior vena 

 cava. It is formed by the union of two tributaries. The great cardiac or left 

 coronary vein (V. cordis magna) ascends in the left longitudinal groove and turns 

 backward in the coronary groove, in which it winds around the posterior border of 

 the heart to the right side and joins the coronary sinus. The middle cardiac or 

 right coronary vein (V. cordis media) ascends in the right longitudinal groove and 

 joins the coronary sinus, or opens separately into the atrium just in front of the 



^ Most of the veins are depicted in the illustrations of the section on the arteries, to which 

 reference is to be made. Many satellite veins which are homonymous with the arteries which 

 they accompany, and present no important special features, are not described here. 



