1570 A MANUAL OF ANATOMY 



can therefore be laid down for the guidance of the dissector. He will 

 certainly find the phrenic nerve descending upon the scalenus anticus muscle. 

 Piercing the scalenus medius he should find the following nerves, in order 

 from above downwards : (i) the nerve to the rhomboids; and (2) the upper 

 two roots of the posterior thoracic nervej or external respiratory nerve of Bell. 



The subclavian or supraclavicular triailgle noV falls to be dissected. Its 

 boundaries will by this time be self-evident, as well as the structures forming, 

 and related to, its roof, in connection with which the supraclavicular glands 

 are to be noted. The third part of the subclavian artery must be carefully 

 dissected, as well as the nerve-trunks of the brachial plexus, all emerging 

 from behind the scalenus anticus muscle. Possibly the posterior scapular 

 artery may be found to arise from the third part of the subclavian. The 

 subclavian vein will not be visible, inasmuch as it lies under cover of the 

 clavicle ; neither will the suprascapular vessels. The transverse cervical 

 vessels, however, will be found within the triangle, where the posterior belly 

 of the omo-hyoid is about to disappear beneath the posterior border of the 

 sterno-cleido-mastoid. The relative positions of the upper, middle, and 

 lower nerve-trunks of the brachial plexus to the third part of the subclavian 

 artery are to be made perfectly clear. The formation of the entire plexus 

 is to be made quite manifest. Arising from the front of the upper nerve- 

 trunk will be found the nerve to the subclavius muscle, which is of small 

 size, and descends over the artery and behind the clavicle. The suprascapular 

 nerve, of large size, is to be found arising from the back of the upper nerve- 

 trunk, and taking a course downwards and outwards. 



At this stage the dissectors of the head and upper limb should work in 

 concert, and the clavicle and subclavius muscle should be divided about their 

 centre. After a certain amount of dissection an instructive view will be 

 obtained of (i) the continuity between the third part of the subclavian artery 

 and the first part of the axillary ; (2) the subclavian vein ; (3) the supra- 

 scapular vessels ; (4) the cords of the brachial plexus ; and (5) the infra- 

 clavicular branches of the plexus. 



Anterior Triangle of the Neck. — The deep cervical fascia is to be dissected 

 as far as possible, without going too deeply at the present stage. The supra- 

 sternal space, or space of Burns, is to be examined, and the portion of the 

 deep cervical fascia which extends between the upper part of the anterior 

 border of the sterno-cleido-mastoid and the angle of the inferior maxilla is 

 to be noted. The sterno-cleido-mastoid muscle is to be completely dissected, 

 and its complicated relations studied. The sterno-hyoid, sterno-thyroid, 

 and the anterior belly of the omo-hyoid are also to be dissected, always 

 keeping in view the disposition of the deep cervical fascia. In the dissection 

 of these muscles the descendens cervicis (hypoglossi) nerve is to be exposed. 

 It will be met with either within, or upon, the carotid sheath over the line of 

 the common carotid artery, and in connection with it the loop known as the 

 ansa cervicis (hypoglossi) is to be exposed. It is situated about the centre 

 of the neck, and taking part in it there will be found, coming from behind, a 

 nerve formed by the union of the two rami communicantes cervicis (hypo- 

 glossi) from the second and third cervical nerves. These two rami, however, 

 may join the descendens cervicis separately, and before receiving them it 

 parts with its branch to the anterior belly of the omo-hyoid. The loop itself 

 is to be shown furnishing branches to the sterno-hyoid, sterno-thyroid, and 

 posterior belly of the omo-hyoid. The thyro-hyoid muscle is also to be dis- 

 sected, and the thjrro-hyoid branch of the hypoglossal nerve is to be shown 

 entering the muscle beneath its posterior border. Passing beneath this 

 border there will also be found the internal laryngeal nerve and superior 

 laryngeal artery, which here pierce the thyro-hyoid membrane on their way 

 to the interior of the larynx. 



The structures along the median line of the neck are to be carefully dis- 

 tected at this stage, in connection with the operations of laryngotomy and 

 tracheotomy. In doing so the disposition of the deep cervical fascia must 

 be constantly kept in view, and the following groups of lymphatic glands 

 may as well be disposed of at once, namely, the submaxillary lymphatic 



