34 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 
vertebre (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 
