THE VEINS 585 



the great metatarsal artery. It gives off muscular branches to the dorso-lateral 

 group of muscles of the leg and articular branches to the hock. The peroneal 

 branch (A. peronea) is a variable vessel which descends along the fibula under the 

 lateral extensor; it gives off muscular branches and one which perforates the fascia 

 and divides into ascending and descending cutaneous twigs. 



The perforating tarsal artery (A. tarsea perforans) is given off under cover of 

 the outer tendon of the ixn'oneus tertius. It passes backward through the vascular 

 canal of the tarsus with a satellite vein and unites on the upper part of the sus- 

 pensory ligament with the plantar arteries (or only with the external plantar) to 

 form the plantar arch. 



In well-injected specimens it is seen that there is a fine arterial network (Rete 

 tarsi dorsale) on the flexor surface of the hock, which is formed by twigs from the 

 anterior tibial and lateral tarsal arteries. From it proceed two very slender dorsal 

 metatarsal arteries. The inner one descends in the ftn-row lietween the inner small 

 and large metatarsal bones, and anastomoses usually in the jjroximal part of the 

 metatarsus with the internal superficial plantar metatarsal, uniting sometimes with 

 the deep plantar metatarsal. The external vessel passes down under the periosteum 

 on the anterior face of the large metatarsal bone and becomes lost or joins the large 

 metatarsal artery. 



Sometimes the anterior tibial artcrj' passes unilividcd through the tarsus, gives off the 

 internal deep plantar metatarsal, anil is continued as a very large internal superficial plantar 

 metatarsal along the deep flexor tendon, thus resembling the arrangement in the fore limb. 



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

 and is continued by a large internal 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 passes downwartl and outward under 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 upper part of the large metatarsal bone. It then descends 

 in the groove formed by the apposition of the large and external small metatarsals, 

 inclines inward between the two, and divides on the lower part of the posterior 

 face of the large metatarsal bone into the internal and external digital arteries. It 

 is not usually accompanied by a vein. Beyond this the arterial arrangement is 

 the same as in the thoracic limb. 



THE VEINS 1 

 PULMONARY VEINS ' 

 The terminal pulmonary veins (Vv. pulmonales), usually 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 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 adherent to each other. 



SYSTEMIC VEINS 

 The Veins of the Heart i Figs. 426, 427) 

 The coronary sinus (Sinus coronarius) is a very short bulbous trunk w^hich 

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



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

 reference is to be made. 



