690 



BLOOD-VASCULAR SYSTEM OF THE HORSE 



the dorsal longitudinal ligament. They are continuous in front with the basilar 

 plexus. The}' lie in the grooves on the bodies of the vertebrae and are connected 

 l)y a series of transverse anastomoses which pass between the central part of the 

 bodies of the vertebra; and the dorsal longitudinal ligament or in channels in the 

 bone. They receive veins from the spinal cord, the meninges, and the bodies of the 

 vertebra (Vena; basis vertebra). Through the intervertebral foramina efferent' 

 vessels connect with the occipital, vertebral, intercostal, lumbar, and lateral sacral 

 veins. The veins of the spinal cord are drained by dorsal and ventral longitudinal 



trunks. The ventral vein, which is the smaller, 

 accompanies the ventral spinal artery. 



VEINS OF THE THORACIC LIMB 

 The brachial vein (V. brachialis) (Fig. 566) 

 is the satellite of the extrathoracic part of the 

 brachial artery. It arises at the medial side of 

 the distal end of the shaft of the humerus and 

 ascends in the arm behind the artery under cover 

 of a layer of fascia and the posterior superficial 

 pectoral muscle. At the shoulder it is ventral to 

 the artery, crosses the anterior border of. the first 

 rib, and concurs with its fellow and the two jugu- 

 lars in the formation of the anterior vena cava. 

 The roots of the vein are somewhat variable, but 

 most often four veins in addition to a large ob- 

 lique branch from the cephalic unite in its forma- 

 tion; two or three of these radicles are satellites of 

 the median artery. Its tributaries correspond in 

 general to the branches of the artery, but a few 

 differences are worthy of notice. The thoraco- 

 dorsal vein (V. thoracodorsalis) often joins the 

 external thoracic or the deep brachial vein. The 

 external thoracic vein (V. thoracica externa) "^ is a 

 large vessel which arises in the ventral wall of the 

 abdomen, passes forward (embedded partly in the cutaneus muscle) along the lateral 

 border of the posterior deep pectoral muscle, and joins the brachial vein close to 

 the subscapular or in common with it. It may receive a vein which is the satellite 

 of the external thoracic artery. 



The cephalic vein (V. cephalica) arises at the medial side of the carpus as the 

 continuation of the medial metacarpal vein. It ascends on the deep fascia 

 of the forearm at first in the furrow between the flexor carpi radialis and the 

 radius. Toward the middle of the forearm it inclines gradually forward on the 

 medial surface of the radius, accompanied by a branch of the musculo-cutaneous 

 nerve, and arrives at the insertion of the biceps. Here it detaches a large com- 

 municating branch (Ramus communicans), which passes upward and backward over 

 the medial insertion of the biceps and the median artery and median nerve, 

 and joins the brachial vein. The vein to this point is often termed the internal sub- 

 cutaneous vein of the forearm (V. cephalica antebrachii) . It is continued (as the 

 V. cephalica humeri) in the furrow between the brachiocephalicus and the anterior 

 superficial pectoral muscle with a branch of the inferior cervical artery, crosses the 

 deep face of the cervical cutaneus, and opens into the terminal part of the jugular 

 or the brachial vein. It receives the accessory cephalic vein (V. cephalica accessoria) , 

 which arises from the carpal network, runs upward on the deep fascia along the 



1 Often termed the spur vein. 



Fig. 589. — Vebtebeal Sinuses of Hoese. 

 The vertebral canal ha3 been opened 

 by sawing off the arches. The nerve-roots 

 are cut on one side and the spinal cord 

 turned over to right. 1, Ventral spinal 

 artery; 2, reinforcing branches from verte- 

 bral, intercostal, or lumbar arteries (ac- 

 cording to region); 5, longitudinal verte- 

 bral sinuses; a, ventral surface of spinal 

 cord; h, dura mater (cut) ; c, nerve-roots; 

 d, dorsal longitudinal ligament. (After 

 EUenberger, in Leisering's Atlas.) 



