AETEEIAL H^EMOKKHAGE. 265 



Excess or deficiency in the number of semilunar cusps at the 

 aortic and pulmonary orifices may similarly be due to malforma- 

 tions of the endocardial cushions of the aortic bulb. 



BLOOD VESSELS. 

 HEMORRHAGE. 



Loss of blood may occur from any part of the vascular system. 

 Hence haemorrhage is often divided into the arterial, the capillary 

 and the venous varieties. 



Arterial haemorrhage from a normal vessel is almost always 

 due to a wound of the artery from without rather than a rupture 

 of its walls by the blood pressure from within. The wound which 

 implicates the vessel may be one which passes down to it through 

 the skin or one which is made into it by the sharp edge of a frac- 

 tured bone. Hence it follows that the more superficial the artery, 

 the more likely it is to be injured from the surface, and the closer 

 its proximity to a bone, the greater is its danger of laceration after 

 fracture. 



Except in the case of gun-shot injuries, arteries of the extremi- 

 ties are more commonly wounded than those of the trunk, and 

 the vessels of the upper extremity more frequently than those of 

 the lower. Probably because of their position the radial and 

 ulnar arteries are the most common vessels to be accidentally 

 divided. 



Arteries of Head and Neck. Wounds of the face are apt to 

 be followed by severe haemorrhage from the facial artery or from 

 one or other of its many branches. Crossing the lower border of 

 the mandible immediately in front of the masseter that is, at a 

 point about one-third the distance between the angle and the 

 symphysis menti the vessel passes tortuously towards the angle 

 of the mouth, and then ascends more vertically, to terminate 

 near the inner canthus of the eye. In the opening of a dental 

 abscess in connexion with the lower molars, the artery may 

 be exposed to injury unless the knife is kept close to the 



