GUIDE TO THE HEAD AND NECK i57l 



glands, the suprahyoid or submental glands, and the prelaryngeal gland:5, 

 the latter being met with in the vicinity of the cricoid cartilage, but being 

 sometimes absent. The structures to be attended to along the median line 

 of the neck are as follows, in order from above downwards : (i) the sub- 

 mental triangle ; (2) the body of the hyoid bone, with the great comu on 

 either side ; (3) the thyro-hyoid membrane ; (4) the isthmus (fHDmum Adami) 

 of the thyroid cartilage, above which is the well-marked V-shaped thyroid 

 notch, whilst on either side of it is the expanded ala of the thyroid cartilage ; 



(5) the crico-thyroid membrane, largely concealed on either side by the crico- 

 thyroid muscle, and crossed at its centre by the crico-thyroid arterial arch ; 



(6) the narrow anterior part of the cricoid cartilage ; (7) the trachea ; (8) the 

 isthmus of the thyroid body, usually lying upon the second and third tracheal 

 rings ; and (q) the inferior thyroid plexus of veins, from which there pass 

 downwards the right and left inferior thyroid veins. The superficial mus- 

 cular relations of the trachea are to be carefully noted. The region concerned 

 in laryngotomy is that occupied by the crico-thyroid membrane. The high 

 operation of tracheotomy affects the trachea above the isthmus of the thj^oid 

 body, and the low operation is performed upon the trachea below the isthmus. 

 In connection with the latter part of the trachea the dissector should care- 

 fully note the following points : (i) its gradually increasing depth ; (2) the 

 presence of the inferior thjToid plexus of veins ; (3) the relation to it of the 

 innominate and right common carotid arteries ; and (4) the possible presence 

 of an arteria thyroidea ima at or close to the median line. 



The carotid sheath is next to be dissected, keeping in view that the de- 

 scendens cervicis (hypoglossi) nerve may lie upon it, or be within it. The 

 sheath will be found to be derived from the posterior lamina of the sheath 

 of the stemo-cleido-mastoid muscle. It is to be carefully opened, having 

 previously noted the stemo-cleido-mastoid artery, and its contents displayed, 

 namely, the common carotid artery, the internal jugular vein, and the pneumo- 

 gastric nerve, all in separate compartments. Possibly the descendens cervicis 

 nerve may be within it. The contents of the sheath are to be fully dissected, 

 bearing in mind that the gangliated cord of the sympathetic lies close behind 

 the sheath. In dissecting the internal jugular vein the superior and middle 

 thyroid veins are to be borne in mind as tributaries of it, and the deep cervical 

 glands will be found more or less along its course. An effort should be made 

 to expose the carotid body, which will be found behind the common carotid 

 artery close to its bifurcation. On a level with the thyroid attachment of 

 the thyro-hyoid muscle the external laryngeal nerve will be found, which is 

 to be traced downwards to its distribution, chiefly to the crico-thyroid 

 muscle. 



The digastric muscle is next to be dissected, along with the stylo-hyoid 

 muscle, which lies above its posterior belly, and the hypoglossal nerve, which 

 lies along its lower border, and here gives off the descendens cervicis and 

 thyro-hyoid nerves. In connection with the V-shaped arrangement of the 

 tendon of the digastric and the hypoglossal nerve, which has now passed 

 beneath the digastric tendon, the triangle of Lesser is to be carefully studied. 

 It contains a portion of the lingual artery, Ijring under cover of the hyo-glossus 

 muscle. The three subdivisions of the anterior triangle of the neck are now 

 to be reviewed, namely, the muscular (inferior carotid), cjirotid (superior 

 carotid), and digastric or submaxillary triangles, and their contents noted. 

 The first parts of the external and internal carotid arteries are to be dis- 

 sected, the former as high as the point where it enters the parotid gland. 

 The anterior branches of the external carotid are to be displayed, namely, 

 the superior thyroid, lingual, and facial, in this order from below upwards. 

 The superior thyroid artery is to be completely dissected, and the following 

 branches of it are to be specially noted, namely, the crico-thyroid artery, 

 and the artery of the isthmus of the thyroid body. The facial artery is only 

 to be dissected as far as the base of the inferior maxilla. Its relation to the 

 submaxillary gland is to be noted, and its cervical branches shown, namely, 

 inferior palatine, tonsillar, glandular, and submental. The lingual artery is, 

 meanwhile, only to be dissected at its origin, and in the first part of its course. 



