DISSECTION OF THE HEAD AND NECK. 149 



the parotid it is joined by a large branch — the submaxillary vein; and 

 it then passes into the jugular furrow, in which it descends to the 

 entrance to the chest. The upper boundary of the furrow, it will now 

 be observed, is formed by the mastoido-humeralis, and the lower by the 

 sterno-maxillaris. In the upper half of this groove the vein rests on the 

 subscapulo-hyoideus muscle, which there 'separates the vessel from the 

 carotid artery ; but in the lower half the vein rests on the side of the 

 • trachea, and is in direct contact with the carotid, which lies above and 

 slightly internal to it. The jugular of the left side differs from the 

 right in being related, in the lower part of the groove, to the oesophagus 

 as well as the trachea. At the entrance to the chest the right and left 

 jugulars unite with one another and with the axillary veins, thus form- 

 ing the initial portion of the anterior vena cava. 



The jugular receives, in the part of its course now exposed, the 

 following branches : — 



1. The Submaxillary or Facial vein, which joins the jugular at an 

 acute angle in which lies the inferior extremity of the parotid gland. 



2. The Thyroid vein, bringing blood from the thyroid body and 

 larynx. 



3. Innominate cutaneous, muscular, oesophageal, and tracheal branches, 

 whose disposition is not constant. 



4. The Cephalic vein, which enters the jugular near its termination. 

 The Sterno-maxillaris (Plate 27). This muscle corresponds to the 



inner portion of the sterno-mastoid of man. It crises from the carini- 

 form cartilage of the sternum, and is inserted by a flat tendon into the 

 angle of the inferior maxilla. In the lower half of the neck the muscle 

 lies below the trachea, and covers the sterno-thyro-hyoideus muscle. 

 In this position the right and left muscles are in contact, but about the 

 middle of the neck they diverge, and cross obliquely upwards and 

 forwards over the trachea and the subscapulo-hyoideus muscle. Its 

 terminal tendon is included between the parotid and submaxillary glands. 

 The upper edge of the muscle forms the lower boundary of the jugular 



» furrow. In its lower part the muscle is thick and rounded, but it 

 becomes more slender and flattened as it is traced upwards. 



Action. — To depress (flex) the head or give it a lateral inclination,' 

 according as the right and left muscles act singly or in concert. 



-k The Sterno-thyro-htoideus (Plates 27 and 28). This is a long and 

 slender muscle, extending along the lower face of the trachea, and closely 

 applied along the middle line to its fellow of the opposite side. It takes 

 origin from the cariniform cartilage of the sternum. About the middle 

 of the neck its muscular substance is interrupted by a short tendinous 

 portion, rendering the muscle digastric. Above this central tendon the 

 muscle divides into two portions. The outer or thyroid band passes 

 obliquely outwards and forwards between the trachea and the sub- 



