THE ARTERIES 129 



Neurectomy of the Fifth Nerve. — Neurectomy of this nerve has been 

 practised by Williams, of Cornell University, and others in the treatmen 

 of " Involuntary shaking of the head." The animal should be placed 

 under a general anesthetic, and it is necessary to remove the bridle, 

 halter or head-collar, in order to clear the operation area. 



By careful manipulation of the levator labii superioris proprius muscle, 

 the infra-orbital foramen may be located. An incision in the direction 

 of the length of the muscle should be made about an inch long, down- 

 wards and forwards from the superior border of the foramen, which is 

 placed two inches forwards from the inferior extremity of the zygomatic 

 ridge. The incision is carried through the subcutaneous fascia and the 

 tendinous portion of the levator labii superioris alsque nasi muscle. 

 Through this opening a finger should be introduced, and the proprius 

 muscle, together with the angular branches of the submaxillary artery and 

 vein which lie on its superficial aspect, may be pushed aside, since, as 

 already stated, this muscle is very loosely attached to the subjacent 

 bones. 



The nerve is thus brought into view, and it should be clearly exposed 

 by carefully dissecting away all the surrounding connective tissue. The 

 nerve is then divided as it is leaving the infra-orbital foramen, and the 

 distal end seized with a pair of artery forceps, care being taken to 

 include between the jaws of the forceps all the branches of the nerve. 

 About an inch of the nerve is thus excised. 



Particular attention should be directed to asepsis, since a not un- 

 common sequel is said to be a severe neuritis of the proximal end of 

 the nerve due to septic infection. 



THE ARTERIES 

 Synopsis of Origin, Distribution and Anastomoses 

 The Common Aorta. — This is the enormous arterial trunk which 

 extends upwards from the conus arteriosus of the left ventricle. It is 



