SPECIAL ANATOMY. ]17 



surface of the branch of the inferior maxilla. At its origin 

 it is tendinous, and through its substance run strong tendi- 

 nous bands, which are inserted below into irregular ridges ; 

 these bands are a provision for the constant closure of the 

 jaws when not required to be separated in mastication or 

 otherwise, for this muscle, with temporalis, pterygoideus, 

 and masseter internus serve to close the month. In many 

 other- situations we shall observe tendinous bands running 

 throughout the whole length of auiscles to support weight, 

 without the active contraction of muscular fibre which 

 would weary. 



Along the posterior part of the superior margin of mas- 

 seter externus we see the temporal artery with an 

 accompanying vein, which vein is sujDeriorly placed. This 

 artery is one of the three terminal trunks of the external 

 carotid, and after winding round the angle of the jaw 

 posteriorly, proceeds for about two inches on the external 

 surface of this muscle, and then dips down into its sub- 

 stance ; the pulse is frequently taken at this artery. Along 

 the anterior margin of the masseter externus run the 

 submaxillary artery and vein, with the duct of the parotid 

 salivary gland. The artery is almost invariably the most 

 anteriorly situated, but the position of the vein and duct is 

 not constant. At first in contact with the inferior maxillary 

 bone they next pass over retractor labii inf erioris, when the 

 artery gives off a branch running forwards, the inferior 

 labial and several branches, the anterior masseteric, which 

 run from it posteriorly to the masseter muscle. They then 

 run on to buccinator and caninus, the muscles which form 

 the cheek ; about the centre of this muscular mass the duct 

 dips between the muscular fibres, and having proceeded a 

 short distance beneath the buccal mucous membrane, opens 

 into the mouth at a small eminence or papilla situated 

 opposite the space between the second and third molar 

 teeth (but the position of this opening is not constant). At 

 the anterior extremity of the zygomatic spine the sub- 

 maxillary artery divides into the superior labial and facial. 

 This division occurs just after the vessel has passed over 

 the originating tendon of retractor labii superioris ; the 

 superior labial branch runs forward, being mingled with 

 the fibres of the superior maxillary division of the fifth 

 cranial nerve, which here emerge from the infra-orbital 

 foramen, and run to the upper lip. With these it pierces 



