THE ANTERIOR PART OF THE NECK 133 



and internal carotid arteries. Dissect in the interval between 

 the vein and the arteries and secure the vagus nerve, which 

 lies deeply. 



Remove the remains of the fascia from the carotid arteries 

 and the internal jugular vein, but avoid injury to the hypo- 

 glossal nerve and its branches ; and note the presence of 

 the upper deep cervical lymph glands which lie on the 

 superficial surfaces of the great arteries and the internal 

 jugular vein. The glands are sometimes very large, and the 

 dissectors should remember that they receive lymph from the 

 face, the mouth and tongue, the posterior part of the nose and 

 the upper part of the pharynx. After the large vessels are 

 cleaned, remove the fascia from the branches of the external 

 carotid artery and the twigs they give off, so far as they lie in 

 the region of the carotid triangle. Commence with the superior 

 thyreoid. Immediately after its origin it gives off a small infra- 

 hyoid branch, then a laryngeal branch which accompanies the 

 internal laryngeal branch of the superior laryngeal nerve ; and, 

 just before it disappears under cover of the anterior belly of the 

 omo-hyoid, a sterno-mastoid branch arises from its posterior 

 border and runs downwards and backwards, along the upper 

 border of the omo-hyoid, across the superficial aspect of the 

 common carotid artery and the internal jugular vein. Next, 

 clean the lingual artery and note its small supra-hyoid branch. 

 The external maxillary artery gives off no branches in the carotid 

 triangle, but a sterno-mastoid branch of the occipital artery will 

 usually be found passing downwards and backwards, superficial 

 to the loop of the hypoglossal nerve. Push the lower border of 

 the parotid gland upwards, and immediately under cover of it, 

 at the level of the angle of the mandible, secure the accessory 

 nerve, as it emerges from under cover of the posterior belly of 

 the digastric and crosses superficial to the internal jugular vein. 

 It is sometimes accompanied by an additional branch to the 

 sterno-mastoid from the occipital artery. 



The floor or medial boundary of the carotid triangle is 

 formed by the upper part of the thyreo-hyoid muscle, the 

 posterior part of the hyoglossus and the middle and inferior 

 constrictors of the pharynx. The latter two muscles cannot 

 be displayed at present, -but the thyreo-hyoid is exposed below 

 the greater cornu of the hyoid bone, and part of the hyoglossus 

 can be seen in the angle between the greater cornu of the hyoid 

 and the lower part of the posterior belly of the digastric. 



The Muscular Triangle. When the deep fascia which 

 covers the muscular triangle is removed, portions of three 

 muscles are brought into view. Postero- superiorly is the 

 anterior belly of the omo-hyoid ; more anteriorly and on 

 the same plane is the sterno-hyoid ; and below and anterior to 

 the sterno-hyoid, but on a deeper plane, is a small part of the 

 sterno-thyreoid. 



The muscles mentioned may be considered to form the 



