FRACTURE OF THE LOWER JAW. 343 



to the mucous lining of the sinus, it was necessary to dissect con- 

 siderable flaps in order to cover the defects. The parts were carefully 

 shaved and disinfected, and a slender paring removed from the edges 

 of the wound to ensure fresh surfaces for union. In the first case 

 an incision was carried from d successively to points /, g, and h, and 

 the flap dissected free from subjacent tissues, leaving it connected 

 with the rest of the skin only at a h. The prolongation to / and 

 the large size of the flap were necessitated by the knowledge that 

 contraction would occur. The edges a c d f were then brought in 

 contact with a b c, and / g were united to c d with closely placed 

 sutures. Healing of the flap was perfect, and the exposed surface 

 h d Z 1 g soon granulated and was finally covered by skin. 



When, in consequence of injuries in the neighbourhood of the 

 neck or withers, large indolent wounds are left, healing can often 

 be effected by incising the skin and subcutaneous tissues on either 

 side of the wound, dissecting the skin free so as to form flaps, and 

 uniting these in the middle line as indicated in Figs. 324 and 325. 



(2.) FRACTURE OF THE LOWER JAW. 



Of all the bones of the head the under jaw is the most frequent 

 seat of fracture : this is true of all classes of animals, and notably 

 of the horse. The causes are external violence, kicks and falls ; 

 occasionally the excessive action of the muscles of mastication, as 

 when the mouth gag is applied to horses suffering from brain disease, 

 or in the simultaneous application of the mouth gag and twitch. 

 Hertwig considers that, under these circumstances, the animals are 

 unable rightly to estimate the degree of contraction of the masseter 

 muscles. Hering saw a case in the horse, caused by the clumsy use 

 of the tooth chisel. In dental operations fractures may occur under 

 the same circumstances as in the upper jaw. Transverse fracture 

 of the body of the jaw in calves not infrequently results from violent 

 manipulation during delivery. In a similar way fracture of the 

 symphysis of the lower jaw may be caused by parturition hooks being 

 inserted in the angle behind the body of the jaw. In staghounds they 

 result from the prey striking out at the moment when the dog has 

 fastened on to the hind limb. 



The fracture is sometimes subcutaneous, and remains confined 

 to one branch of the lower jaw ; but not infrequently both branches 

 break, and usually at the neck, where teeth are wanting. Vormeng 

 noted breakage of both branches in the middle line, an accident which 

 occurs more frequently in foals than in older animals. Fractures 



