THE WITHERS 31 
their cartilaginous summits, their backward 
direction, their connecting media and the con- 
tiguous musculature. 
Blood Vessels 
The withers receives its blood supply chiefly 
from two sources: the dorsal and the deep 
cervical arteries. Both are direct radicals of 
the brachial arteries, or more correctly speak- 
ing, the left one arises from the left brachial 
artery and the right one from that part of the 
same vessel on the right side while it still bears 
the name brachiocephalic artery. The origin 
of both is within the thorax. The dorsal 
enters the region of the withers through the 
second intercostal space and the deep cervical, 
through the first. Both of them leave the 
thorax near the bodies of the vertebre. Their 
extra-thoracic distribution alone interests us, 
in surgery of the withers. 
Extra-thoracic distribution of the dorsal 
artery. After emerging from the thorax 
through the second intercostal space it passes 
under the longissimus dorsi in an upward and 
backward direction, soon dividing into several 
branches. The largest anterior branch passes 
forward and upward under the splenius; 
extending branches anastomose with the deep 
cervical or are lost in the deep muscles of 
