232 HEAD AND NECK 



the upper border of the great cornu. Remove the fascial sheath from the 

 superficial surfaces of the lower parts of the internal and external carotid 

 arteries, and from the upper part of the common carotid artery. Note that 

 the latter divides into the two former at the level of the upper border 

 of the thyreoid cartilage, and that the external carotid is at first medial 

 and anterior to the internal carotid. 



Five branches may spring from the external carotid in the carotid 

 triangle, three from its anterior surface : the superior thyreoid, the lingual 

 and the external maxillary ; one from its medial surface, the ascending 

 pharyngeal ; and one from its posterior surface, the occipital ; but not un- 

 commonly the occipital and the external maxillary arise beyond the limits 

 of the carotid triangle under cover of the posterior belly of the digastric. 

 The superior thyreoid springs from the front of the lower part of the ex- 

 ternal carotid below the level of the great cornu of the hyoid and runs 

 downwards to the lower angle of the carotid triangle, where it disappears 

 under cover of the anterior belly of the omo-hyoid. The lingual arises 

 immediately above the level of the tip of the great cornu. It runs an- 

 teriorly above the level of the cornu, forming a loop, convex upwards, 

 which lies deep to the hypoglossal nerve ; and it disappears under cover 

 of the posterior border of the hyoglossus muscle. The ascending pharyngeal 

 branch, which springs from the medial surface of the lower end of the ex- 

 ternal carotid, ascends on a deeper plane, between the external and in- 

 ternal carotids and the wall of the pharynx, and will be followed at a later 

 stage of the dissection. The external maxillary and the occipital arise 

 immediately below the posterior belly of the digastric and almost at 

 once disappear under cover of the muscle ; not uncommonly they 

 arise under cover of its lower border. Before proceeding to clean the 

 branches of the external carotid secure the internal and external laryngeal 

 branches of the superior laryngeal branch of the vagus nerve. The internal 

 branch will be found in the posterior part of the thyreo-hyoid interval below 

 the great cornu of the hyoid bone and behind the posterior border of the 

 thyreo-hyoid muscle, beneath which it disappears. It is accompanied by 

 the laryngeal branch of the superior thyreoid artery. The external branch 

 is more difficult to find ; but, if the superior thyreoid artery and the upper 

 part of the common carotid are displaced posteriorly, the nerve will be 

 found, lying deep to them, in the fascia which covers the anterior part of the 

 inferior constrictor muscle. Remove the fascia from the surface of the in- 

 ternal jugular vein, which overlaps the posterior borders of the common 

 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 hypoglossal 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 posteriorly, along the upper border of the omo-hyoid, across the super- 

 ficial aspect of the common carotid artery and the internal jugular vein. 



