106 The Mon tli 



borders are fused with the ingrowing maxillary parts, the fissure is 

 exactly median. This condition, however, is extremely rare. 1 



The operation for hare-lip consists in freshing the sides of the cleft, 

 freeing the maxillary attachments of the lip, and adjusting the cleft by 

 stitches and strapping, arrangements being made that the muscles do 

 not pull the edges asunder. 



The cheeks, like the lips, with which they are continuous, consist 

 of skin and mucous membrane, with intervening muscular tissue, 

 namely, buccinator, zygomatici, platysma, and masseter. They con- 

 tain, also, a good deal of fat ; and beneath the mucous membrane are 

 minute salivary glands resembling those of the lips. 



On the mucous lining of the cheek, opposite the second molar 

 tooth of the upper jaw, is a flat papilla upon which is the opening of 

 the parotid duct, which has just traversed the buccinator. To save 

 himself the annoyance caused by the flow of saliva during certain 

 dental operations, the dentist sometimes stuffs a piece of cotton-wool 

 between the upper jaw and the cheek so as to block the orifice of the 

 duct. 



The buccinator arises from the alveolar process above the molar 

 teeth of the upper, and below those of the lower jaw ; and, posteriorly, 

 in the space between the jaws, from a fibrous seam connecting the 

 muscle with the front of the superior constrictor the pterygo-maxillary 

 ligament. Thus the mouth is directly continuous with the pharynx. 



Action. The buccinator helps the man to ' blow his own trumpet ' ; 

 it is thus a muscle of expression, and is, therefore, under the control 

 of the facial nerve. Its chief office is to gather up the half-chewed 

 food which falls outwards from between the molar teeth, and to push 

 it again into the mill. When the facial nerve is paralysed the food 

 persistently collects in the cheek, whence the patient has to dislodge 

 it with his finger. So useless is the muscle in facial paralysis that 

 there can be no manner of doubt that the branches which the muscle 

 gets from the inferior maxillary nerve (p. 63) are but sensoiy. 



Relations. The muscle is covered by skin, superficial fascia, and 

 the muscles which draw the angle of the mouth downwards, back- 

 wards, and upwards ; it is crossed by the facial artery and vein, 

 and by branches of the facial and buccal nerves. Stenson's duct 

 passes through it opposite the second upper molar. A good deal of 

 fat is packed in between it and the anterior border of the masseter ; 

 in phthisis this is gradually consumed and the cheeks sink in. Behind 

 the muscle is the pharynx ; in front is the orbicularis, and lining it is 

 the mucous membrane of the mouth. 



Pterygro-maxillary ligament. The student is advised to pass 

 the tip of his index-finger behind, and a little to the inner side of, the 

 last molar tooth, where he will find a band beneath the mucous 

 membrane. The more widely the mouth is opened, the tighter the 



1 See case reported by Bernard Pitts, "Z ancet, 1889. 



