524 ANGIOLOGY 





The external jugular vein at first drains the region behind the ear (posterior 

 auricular) and enters the primitive jugular as a lateral tributary. A group of veins 

 from the face and lingual region converge to form a common vein, the linguo-facial, 1 

 which also terminates in the primitive jugular. Later, cross communications 

 develop between the external jugular and the linguo-facial, with the result that 

 the posterior group of facial veins is transferred to the external jugular. 



THE THORACIC CAVITY. 



The heart and lungs are situated in the thorax, the walls of which afford them 

 protection. The heart lies between the two lungs, and is enclosed within a fibrous 

 bag, the pericardium, while each lung is invested by a serous membrane, the pleura. 

 The skeleton of the thorax, and the shape and boundaries of the cavity, have already 

 been described (page 117). 



The Cavity of the Thorax. The capacity of the cavity of the thorax does not 

 correspond with its apparent size externally, because (1) the space enclosed by 

 the lower ribs is occupied by some of the abdominal viscera; and (2) the cavity 

 extends above the anterior parts of the first ribs into the neck. The size of the 

 thoracic cavity is constantly varying during life with the movements of the ribs 

 and diaphragm, and with the degree of distention of the abdominal viscera. 

 From the collapsed state of the lungs as seen when the thorax is opened in the dead 

 body, it would appear as if the viscera only partly filled the cavity, but during 

 life there is no vacant space, that which is seen after death being filled up by the 

 expanded lungs. 



The Upper Opening of the Thorax. The parts which pass through the upper 

 opening of the thorax are, from before backward, in or near the middle line, the 

 Sternohyoideus and Sternothyreoideus muscles, the remains of the thymus, the 

 inferior thyroid veins, the trachea, esophagus, thoracic duct, and the Longus 

 colli muscles; at the sides, the innominate artery, the left common carotid, left 

 subclavian and internal mammary arteries and the costocervical trunks, the 

 innominate veins, the vagus, cardiac, phrenic, and sympathetic nerves, the greater 

 parts of the anterior divisions of the first thoracic nerves, and the recurrent nerve 

 of the left side. The apex of each lung, covered by the pleura, also projects 

 through this aperture, a little above the level of the sternal end of the first rib. 



The Lower Opening of the Thorax. The lower opening of the thorax is wider 

 transversely than from before backward. It slopes obliquely downward and back- 

 ward, so that the thoracic cavity is much deeper behind than in front. The dia- 

 phragm (see page 404) closes the opening and forms the floor of the thorax. The 

 floor is flatter at the center than at the sides, and higher on the right side than on 

 the left; in the dead body the right side reaches the level of the upper border of 

 the fifth costal cartilage, while the left extends only to the corresponding part 

 of the sixth costal cartilage. From the highest point on each side the floor slopes 

 suddenly downward to the costal and vertebral attachments of the diaphragm; 

 this slope is more marked behind than in front, so that only a narrow space is left 

 between the diaphragm and the posterior wall of the thorax. 



THE PERICARDIUM. 



The pericardium (Fig. 489) is a conical fibro-serous sac, in which the heart and 

 the roots of the great vessels are contained. It is placed behind the sternum and 

 the cartilages of the third, fourth, fifth, sixth, and seventh ribs of the left side, 

 in the mediastinal cavity. 



Lewis, American Journa of Anatomy, February, 1909, No. 1, vol. ix. 



