84 FISTULA AND POLL-EVIL 



cervicis in the region of fistula of the 

 withers are often enlarged into vessels of con- 

 siderable dimensions. 



The vertebral artery, — The vertebral artery 

 which emerges from the thorax in front of the 

 first rib passes between the longus colli and 

 the scalenus, and thence along the vertebral 

 column through the foramina transversaria. At 

 the axis it anastomoses with the occipital and 

 along its course supplies numerous branches 

 to the musculature, of both the dorsal and 

 ventral cervical regions. The former anasto- 

 moses freely with branches of the deep cervical. 



This artery is of no great importance in 

 surgery of the withers on account of its deep, 

 protected location. That its branches are 

 capable of undergoing enlargement must, 

 however, be considered in operations invading 

 the region of the vertebral column, as for 

 example in attempts to establish a drainage 

 of abscess cavities resting on the bodies of the 

 vertebrae (cervical fistula). 



The Nerves 

 The nerves of the withers are both cranial 

 and spinal. Sensation is supplied by the dor- 

 sal branches of the thoracic and cervical spinal 

 nerves while the motor supply is derived not 

 only from those mixed nerves but also from 



