76 EXEKCISE XII 



masseter muscle covering the posterior part of the mandible. The field of 

 structures thus exposed is mainly a muscular one, but at the posterior lateral 

 part of it, and close median to the angle of the jaw, can be seen, lying in an 

 area between two veins which meet behind it to a- trunk receiving the hyoid 

 vein, two large lymphatic glands covered by a smooth tough capsule. The 

 muscles seen are the mylohyoid in the median field overlapped laterally by the 

 digastric. The latter at a point in its median edge opposite the lymphatic 

 glands shows a whitish structure, the tendinous intersection between its 

 anterior and posterior bellies ; this intersection lies about -5 cm. in front of 

 a transverse line drawn between the angles of the jaw. Note the transverse 

 direction of the fibres of mylohyoid, and the antero-posterior direction of those 

 of digastric. Make out the delicate dentated tendinous intersection between 

 right and left halves of mylohyoid as exposed along the anterior half of the 

 median edge of the wound ; make out also the posterior border of the 

 mylohyoid. At the posterior edge of mylohyoid and plunging forward and 

 medianward under it, but also visible through the muscle, note a large nerve- 

 trunk, hypoglossal. Beginning at the hinder edge of the muscle close 

 to, but without injuring, hypoglossal nerve, cut through the thin sheet-like 

 mylohyoid near to the median line and right up to the anterior end of the 

 wound. Carefully reflect the muscle laterally along with the digastric quite 

 to the ramus of the jaw for the anterior two-thirds of the length of this latter. 

 In thus reflecting the mylohyoid and digastric there comes into view 

 (PI. VI, fig. 2), between them on the lateral side and the tongue muscles on the 

 median side, the lingualis nerve crossing transversely the ducts of the retro- 

 lingual and submaxillary grands. A small vein usually comes from the tongue 

 and passes across the ducts to perforate mylohyoid about 6 mm. anterior to the 

 lingualis. This must be double-tied and severed between the ligatures. The 

 mylohyoid and digastric should now be detached in front from the horizontal 

 ramus of the jaw, starting from a point about 1 cm. from the symphysis and 

 going backward as far as the anterior edge of masseter muscle. Retract the 

 muscles by a heavy clip-weight laterally. Lingualis nerve can be followed 

 deeply under the ramus of the jaw. Of the two salivary ducts running forward 

 close together and parallel with one another in the valley between ramus of jaw 

 and the muscles of the tongue, the median is Wharton's (submaxillary), the 

 other is the retrolingual. Do not clear the ducts by dissection. 



Obs. 54. [IV. Paint a little dilute acetic acid over the mucous surface of the 



Beflex salivary tongue : this often causes an increased flow of saliva by reflex action, the 

 efferent nerve being the corda tympani, the secretory nerve you are going to 

 excite electrically. 



secretion. 



