THE VEINS—PULMONARY 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 down under the periosteum on the dorsal face of 
the large metatarsal bone and becomes lost or jos the great metatarsal artery. 
In rare cases the anterior tibial artery passes undivided through the tarsus, gives off the 
medial deep plantar metatarsal, and is continued as a very large medial superficial plantar meta- 
tarsal along the deep flexor tendon, thus resembling the arrangement in the forelimb. 
In a few cases the perforating tarsal is a large vessel, directly continuing the anterior tibial, 
and is continued by a large medial deep plantar metatarsal. The great metatarsal is then small. 
Other 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! 
PULMONARY VEINS 
The pulmonary veins (Vy. pulmonales), usually seven or eight in number, 
return the aérated blood from the lungs and open into the left atrium of the heart. 
They are destitute of valves. Their tributaries 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 (VY. 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 
tight 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 
1 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. 
