98 DISSECTION OF THE SUBMAXILLARY REGION. 



of that muscle. In front of it is the anterior belly of the digastric ; and 

 behind is the stylo-maxillary ligament separating it from the parotid. 

 Occupying a position somewhat below the side of the jaw, the gland is 

 very near the surface, being covered only by the integuments and pla- 

 tysma, and the deep fascia. 



In structure the submaxillary resembles the parotid gland (p. 42) ; and 

 its duct duct of Wharton issuing from the deep process, extends beneath 

 the mylo-hyoid muscle to the mouth. 



Dissection. To see the mylo-hyoid muscle, detach the anterior belly 

 of the digastric from the jaw, and dislodge without injury the submaxillary 

 gland from beneath the bone. 



The MYLO-HYOID MUSCLE (tig. 33, 3 ) is triangular in shape, with the 

 base at the jaw and the apex at the hyoid bone, and unites along the 

 middle line with its fellow of the opposite side. It arises from the mylo- 

 hyoid ridge on the inner surface of the lower jaw as far back as the last 

 molar tooth; and is inserted into the middle of the body of the os hyoides, 

 as well as into a central tendinous band between that bone and the jaw. 



On the cutaneous surface lie the digastric muscle, and the submaxillary 

 gland, the facial artery with the submental offset, and its own branch of 

 nerve and artery. Its fibres are frequently deficient near the jaw, and 

 allow the next muscle to be seen. Only the posterior border is unattached, 

 and round it a piece of the submaxillary gland winds. The parts in con- 

 tact with the deep surface of the muscle will be perceived after the under- 

 mentioned dissection has been made. 



Action. The lower jaw being fixed the muscle approaches the os hyoides 

 to the ja\v, enlarging the pharynx preparatory to swallowing. 



With the hyoid bone immovable, the mylo-hyoideus can help in de- 

 pressing the jaw, and opening the mouth. 



Dissection. To bring into view the muscles beneath the mylo-hyoid, 

 and to trace the vessels and nerves to the substance of the tongue (as in 

 figure 23), the student should first divide the facial vessels on the jaw, 

 and remove them with the superficial part of the submaxillary gland; but 

 he should be careful to leave the deep part of the gland which turns be- 

 neath the mylo-hyoideus, because the small submaxillary ganglion is in 

 contact with it. Next he should cut through the small branches of ves- 

 sels and nerve on the surface of the mylo-hyoideus; and detaching that 

 muscle from the jaw and its fellow, should throw it down to the os hyoides, 

 but without injuring the genio-hyoid muscle beneath it. 



Afterwards the bone is to be sawn through on the right side of the 

 muscles attached to the symphysis, the soft parts covering the lower jaw 

 having been previously cut. The side of the jaw, which will then be 

 loose (for the ramus of the bone has been sawn before), is to be raised to 

 see the parts beneath, and it may be fastened up out of the way with a 

 stitch; but it should not be detached from the mucous membrane of the 

 mouth. 



The apex of the tongue is to be now pulled well out of the mouth over 

 the upper teeth, and fastened with a stitch to the septum of the nose, 

 whilst the left half of the jaw is to be drawn down forcibly with hooks. 

 The scalpel should be then passed from below upwards between the sawn 

 surfaces of the bone, for the purpose of dividing a strong band of the 

 mucous membrane of the mouth; and it should be carried onwards along 

 the middle line of the tongue to the tip. 



By means of a stitch the os hyoides may be fastened down, to make 



