GUIDE TO THE HEAD AND NECK 1573 



are to be dissected. The tortuous course of the inferior thyroid artery inwards 

 behind the lower part of the carotid sheath is to be noted, and its ascending 

 cervical branch is to be shown. The proximity of the middle cervical ganglion 

 of the sympathetic to the artery is to be borne in mind. The suprascapular 

 artery is to be followed outwards, and its medullary branch to the clavicle 

 is to be looked for. The transverse cervical artery, like the suprascapular, 

 above which it lies, is to be followed outwards. The suprascapular and 

 transverse cervical have been in part previously dissected. 



The second part of the subclavian artery is to be exposed by dividing and 

 reflecting the scalenus anticus muscle, behind which it lies, whilst the sub- 

 clavian vein lies in front of that muscle. At this stage the mode of formation 

 of the brachial plexus, and the relations of its nerve-trunks to the sub- 

 clavian artery are to be revised. The only branch from the second part of 

 the subclavian artery to be dissected is the superior intercostal artery, which, 

 however, usually arises from the first part of the artery on the left side. To 

 see this vessel on the right side it will be necessary to draw the second part 

 of the subclavian artery well forwards and downwards, because the superior 

 intercostal arises from its posterior and upper aspect. Thereafter the vessel 

 descends in front of the neck of the first rib to supply the first and second 

 intercostal spaces, but, before it does so, the deep cervical artery is to be 

 shown arising from it, and taking a backward course between the seventh 

 cervical transverse process and the neck of the first rib. In an earlier stage 

 of the dissection this vessel has been seen ascending upon the semispinalis 

 colli muscle, under cover of the complexus, and anastomosing with the ramus 

 princeps cervicis of the occipital from the external carotid. 



The apex of the lung, covered by the dome of the pleura, is Kb be very care- 

 fully noted, and attention is to be given to Sibson's fascia. This fascia will 

 be found to extend from the front of the transverse process of the seventh 

 cervical vertebra to the inner border of the first rib. 



Suprahyoid Region. — The dissection of the digastric or submaxillary triangle 

 is now to be overtaken in so far as it can be prior to section of the mandible. 

 The superficial part of the submcixillciry gland, of considerable bulk, will first 

 receive attention. Passing downwards over it the dissector vntII find the 

 facial vein, and more or less embedded in its upper and outer part he will 

 find the facial artery on its way to the face. The superficial part of the 

 gland is to be turned outwards, and kept out of the way by hooks. There- 

 after the mylo-hyoid muscle is to be dissected, along with the mylo-hyoid 

 nerve and submental artery resting upon it. The distribution of the mylo- 

 hyoid nerve to the mylo-hyoid muscle and anterior belly of the digastric 

 is to be clearly shown, and the median raphe between the two mylo-hyoid 

 muscles is to be made evident. The posterior border of the mylo-hyoid 

 muscle is next to receive attention. Passing beneath this border will be 

 found, in order from below upwards, the hypoglossal nerve, the deep part 

 of the submaxillary gland, and the lingujil (gustatory) nerve. In the back 

 part of the digastric triangle a portion of the parotid gland will be met with, 

 which is separated from the submaxillary gland by the process of the deep 

 cervical fascia known as the stylo-maxillary ligament. 



Structures beneath the Mylo-hyoid Muscle. — To expose these structures 

 requires very careful dissection. The mylo-hyoid muscle is to be separated 

 from its fellow along the median raph6, care being taken not to injure the 

 genio-hyoid muscle. It is also to be detached from the body of the hyoid 

 bone, and then the entire muscle is to be reflected upwards towards the 

 mandible. The subsequent steps of this dissection will no doubt be simplified 

 at a later stage when it is in the power of the dissector to divide the mandible 

 at certain points, but no definite hard-and-fast lines can be laid down at this 

 stage. After reflection of the mylo-hyoid muscle the hyo-glossus will be 

 exposed, as well as the stylo-glossus and genio-hyoid. The hyo-glossus is 

 the dissector's landmark. Resting upon its surface he will find the following 

 structures : (i) the hypoglossal nerve, along with the ranine vein, lying close 

 to the hyoid bone ; (2) the deep part of the submaxillary gland and Wharton's 

 duct, lying above the hypoglossal nerve ; and (3) the lingual nerve, highest 



