to HEAD AND NECK 



nasal septum is frequently difficult to display. It springs 

 from the superficial fibres of the upper part of the orbicularis 

 oris, and is inserted into the anterior part of the septum of 

 the nose. It depresses the septum and reduces the antero- 

 posterior diameter of the anterior nasal aperture. The name 

 indicates the action of the muscle, which is supplied by the 

 facial nerve. 



The Muscles of the Mouth and Cheeks. The muscles of 

 this group form two layers, a superficial and a deep. Those 

 of the superficial group are the orbicularis oris, quadratus 

 labii superioris, zygomaticus, triangularis, risorius, quadratus 

 labii inferioris ; those of the deeper group are the buccinator, 

 caninus, incisivus superior and inferior, and the mentalis. 

 All, with the exception of the orbicularis oris, are bilateral. 

 Only the members of the superficial group are at present 

 displayed ; the deeper muscles will be dissected after the 

 superficial vessels and nerves have been cleaned and studied. 



Orbicularis Oris. The orbicularis oris is the sphincter 

 muscle of the oral aperture. It lies in the substance of the 

 lips, and consists of a deeper layer of fibres which are arranged 

 in concentric ellipsoidal rings, and a series of superficial fibres 

 into which all the other muscles of the lips and cheeks con- 

 verge. The details of its formation cannot be understood 

 until the attachments of the other muscles have been studied 

 (see p. 21). It is supplied by the facial nerve. 



Musculus Quadratus Labii Superioris. The quadratus 

 labii superioris possesses three heads a zygomatic, an infra- 

 orbital, and an angular. 



The zygomatic head (O.T. zygomaticus minor] springs 

 from the anterior part of the facial surface of the zygomatic 

 bone, under cover of the lower lateral part of the orbicularis 

 oculi. It runs downwards and forwards, and either joins 

 the infra-orbital head or is inserted into the lateral part of the 

 upper portion of the orbicularis oris and into the adjacent 

 part of the skin of the upper lip. 



The infra -orbital head (O.T. levator labii superioris 

 proprius) arises from the whole length of the infra-orbital 

 border, under cover of the orbicularis oculi. It is inserted 

 into the upper lateral part of the orbicularis oris and the 

 skin of the upper lip (Fig. 2). 



The angular head (O.T. levator labii superioris alceque 

 nasi] springs from the frontal process of the maxilla. It 



