STERNO-CLEIDO-MASTOIDEUS. 71 



sight; whilst a little lower down, with the descending branches of the 

 thyroid artery, is the external laryngeal branch of that nerve. 



Glands in the space. Two. glandular bodies, the subrnaxillary, n , and 

 thyroid, 12 , have their seat in this triangular space of the neck. The sub- 

 maxillary gland is situate altogether in front of the vessels, and is partly 

 concealed by the jaw ; and beneath it on the surface of the mylo-hyoideus 

 is the small nerve to that muscle; with the submental artery. By the side 

 of the thyroid cartilage, between it and the common carotid artery, lies the 

 thyroid body beneath the sterno-thyroid muscle: in the female this body 

 is more largely developed than in the male. 



At the base of the space, if the parts were not disturbed, would be the 

 parotid gland, which is wedged into the hollow between the jaw and the 

 mastoid process, and projects somewhat below the level of the jaw. Its 

 connections have been noticed at p. 41. 



Directions. The student has to proceed next with the examination of 

 the individual parts that have been referred to with the triangular spaces. 



Anterior jugular vein. This small vein occupies the middle line of the 

 neck, and its size is dependent upon the degree of development of the ex- 

 ternal jugular. Beginning in some small branches below the chin, the 

 vein descends to the sternum, and then bends outwards beneath the sterno- 

 mastoid muscle, to open into the subclavian vein, or into the external 

 jugular. In the neck the anterior and external jugular veins communicate. 

 There are two anterior veins, one for each side, though one is usually 

 larger than the other; and at the bottom of the neck they are joined by a 

 transverse branch. 



The STERNO-CLEIDO-MASTOID MUSCLE (fig. 15, ') forms the superficial 

 prominence of the side of the neck. It is narrower in the centre than at 

 the ends, and is attached below by two heads of origin, which are separated 

 by an elongated interval. The inner head is fixed by a narrowed tendon 

 to the anterior surface of the first piece of the sternum ; and the outer head 

 lias a wide fleshy attachment to the sternal third of the clavicle. From 

 this origin the heads are directed upwards, the internal passing backwards, 

 and the external almost vertically, and are blended about the middle of 

 the neck in a roundish belly. Near the skull the muscle ends in a tendon, 

 which is inserted into the mastoid process at the outer aspect from base to 

 tip, and by a thin aponeurosis into a rough surface behind that process, 

 and into the outer part of the upper curved line of the occipital bone. 



The muscle divides the lateral surface of the neck into two triangular 

 spaces. On its cutaneous aspect the sterno-mastoid is covered by the com- 

 mon integuments, by the platysma and deep fascia, and by the external 

 jugular vein and the superficial branches of the cervical plexus (across the 

 middle). If the muscle be cut through below and raised, it will be seen 

 to lie on the following parts : The clavicular origin is superficial to the 

 anterior scalenus and omo-hyoid muscles ; and the sternal head conceals 

 the depressors of the hyoid bone, and the common carotid artery with its 

 vein and nerves. After the union of the heads, the muscle is placed over 

 the cervical plexus, and the middle scalenus and elevator of the angle of 

 the scapula ; and near the skull, on the digastric and splenius muscles, the 

 occipital artery, and part of the parotid gland. The spinal accessory per- 

 forates the muscular fibres about the upper third. 



Action. Both muscles acting bend the head forwards; but one muscle 

 turns the face to the opposite side. In conjunction with the muscles at- 



