690 BLOOD-VASCULAR SYSTEM OF THE HORSE 
the dorsal longitudinal ligament. They are continuous in front with the basilar 
plexus. They lie in the grooves on the bodies of the vertebree and are connected 
by a series of transverse anastomoses which pass between the central part of the 
bodies of the vertebree 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 
vertebree (Ven basis vertebree). 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- 
Mars Ales ean Pees lique branch from the cephalic unite in its forma- 
are cut on one side and the spinal cord tion; two or three of these radicles are satellites of 
turned over to right. 1, Ventral spinal the median artery. Its tributaries correspond in 
artery; 2, reinforcing branches from verte- 
bral, intercostal, or lumbar arteries (ac. general to the branches of the artery, but a few 
cording to region); 3, longitudinal verte- differences are worthy of notice. The thoraco- 
oe ade SS arn Age adaintsers dorsal vein (V. thoracodorsalis) often joins the 
d, dorsal longitudinal ligament. (After | @Xternal thoracic or the deep brachial vein. The 
Ellenberger, in Leisering’s Atlas.) 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- 
Fig. 589.—Verresrat Sryuses oF Horse. 
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. 
