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 vertebrae. Their 

 extra- thoracic distribution alone interests us, 

 in surgery of the withers. 



Ecctra-tlioi'acic distiihution 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 



