THE NECK. 17 



being obscured above by the isthmus of the thyroid body, and below by the muscles 

 and the increasing quantity of fat as the air-tube recedes from the surface, the depth 

 of the front of the trachea at the upper border of the sternum amounting to nearly 

 an inch and a half (3'5 cm.). 



The lower part of the epiglottis is placed behind the thyro-hyoid space, and 



still farther back is the upper aperture of the larynx. The rima glottidis is at a 



. lower level, being opposite the middle of the short anterior margin of the thyroid 



cartilage. The lower border of the cricoid cartilage indicates also the termination 



of the pharynx and the commencement of the oesophagus. 



Along the side of the neck, the sterno-mastoid muscle runs obliquely from the 

 mastoid part of the temporal bone to the sternum and clavicle ; its anterior border, 

 forming the hinder boundary of the anterior triangle of the neck, is thick and 

 prominent, and leads down to the strongly marked sternal head, which passes to the 

 front of the manubrium and gives rise, with its fellow of the opposite side, to the 

 deep suprasternal notch (fossa jugularis}. The posterior border of the muscle is 

 thin, and in its upper part does not show on the surface ; inferiorly it becomes 

 evident and is continued into the clavicular head, which is, however, broader and 

 less salient than the sternal origin. A slight depression usually corresponds to an 

 interval between the two heads, and the lower boundary of the depression is formed 

 by the somewhat prominent inner extremity of the clavicle. A needle thrust back- 

 wards in this depression, and in contact with the end of the clavicle, would reach, on 

 the right side, the bifurcation of the innominate artery, on the left, the common 

 carotid arteiy as it passes into the neck. 



The carotid arteries are situated just beneath the anterior border of the 

 sterno-mastoid muscle, their position being indicated more exactly by a line drawn 

 from the sterno-clavicular articulation to a point midway between the angle of the 

 jaw and the tip of the mastoid process. The common carotid artery reaches upwards 

 - as far as, or slightly beyond, the upper border of the thyroid cartilage ; above this 

 level, the external and internal carotids are placed side by side, the external being 

 the more anterior, until they pass beneath the posterior belly of the digastric 

 muscle, the position of which may be indicated by a line drawn from the raastoid 

 process to the fore part of the hyoid bone. If deep pressure be made in the situa- 

 tion of the great vessels opposite the cricoid cartilage, the prominent anterior 

 tubercle of the transverse process of the sixth cervical vertebra (carotid tubercle) can 

 be felt, and the common carotid artery may be compressed against it. This is a 

 little below the spot at which the omo-hyoid muscle crosses the carotid artery, and 

 indicates also the place where the inferior thyroid artery turns inwards, and the 

 vertebral artery usually enters upon its course through the foramina in the transverse 

 processes. 



The lingual artery arises from the external carotid opposite the hyoid bone ; it 

 first forms a small loop with the convexity upwards, then passes forwards along the 

 upper margin of the great cornu of the hyoid just below the level of the hypo- 

 glossal nerve and ranine vein, which are separated from it by the hyo-glossus 

 muscle. At a slightly higher level, the occipital and facial arteries leave the 

 external carotid, the former passing up to the transverse process of the atlas, which 

 may be felt just below and a little in front of the tip of the mastoid process, the 

 latter taking a winding course at first beneath and then above the submaxillary 

 gland to the anterior border of the masseter muscle. The superior thyroid artery, 

 arising below the lingual, runs downwards and inwards near the back of the thyroid 

 cartilage, and sends its crico-thyroid branch across the crico-thyroid space. 



The line of the internal jugular vein is just external to that of the carotid 

 arteries ; the facial vein, more superficial than the artery, courses from the anterior 

 border of the masseter downwards and backwards, to join the main trunk about 



