OF THE HEAD, FACE, AND XECK. 681 



subclavian vein at its angle of junction with the left internal jugular vein. The 

 thoracic duct, at its commencement, is about equal in size to the diameter of a 

 goosequill, diminishes considerably in its calibre in the middle of the thorax, and 

 is again dilated just before its~ termination. It is generally flexuous in its course, 

 and constricted at intervals so as to present a varicose appearance. The thoracic 

 duct not unfrequently divides in the middle of its course into two branches of 

 unequal size, which soon reunite, or into several branches, which form a plexiform 

 interlacement. It occasionally divides, at its upper part, into two branches, of 

 which the one on the left side terminates in the usual manner, while that on the 

 right opens into the right subclavian vein, in connection Avith the right lymphatic 

 duct. The thoracic duct has numerous valves throughout its whole course, but 

 they are more numerous in the upper than in the lower part : at its termination it 

 is provided with a pair of valves, the free borders of which are turned toward the 

 vein, so as to prevent the passage of venous blood into the duct. 



Tributaries. The thoracic duct, at its commencement, receives four or five 

 large trunks from the abdominal lymphatic glands, and also the trunk of the 

 lacteal vessels. Within the thorax it is joined by the lymphatic vessels from the 

 left half of the wall of the thoracic cavity, the lymphatics from the sternal and 

 intercostal glands, those of the left lung, left side of the heart, trachea, and 

 oesophagus; and, just before its termination, it receives the lymphatics of the left 

 side of the head and neck and left upper extremity. 



Structure (Fig. 61). The thoracic duct is composed of three coats, which 

 differ in some respects from those of the lymphatic vessels. The internal coat 

 consists of a single layer of flattened lanceolate-shaped endothelial cells with 

 serrated borders ; of a subendothelial layer, similar to that found in the arteries ; 

 and an elastic fibrous coat, the fibres of which run in a longitudinal direction. 

 The middle coat consists of a longitudinal layer of white connective tissue with 

 elastic fibres, external to which are several laminae of muscular tissue, the fibres of 

 which are for the most part disposed transversely, but some are oblique or 

 longitudinal and intermixed with elastic fibres. The external coat is composed of 

 areolar tissue, with elastic fibres and isolated fasciculi of muscular fibres. 



The Right Lymphatic Duct is a short trunk, about half an inch in length and 

 a line or a line and a half in diameter. It terminates in the right subclavian vein 

 at its angle of junction with the right internal jugular vein. Its orifice is guarded 

 by two semilunar valves, which prevent the passage of venous blood into the duct. 



Tributaries. It receives the lymph from the right side of the head and neck, 

 the right upper extremity, the right side of the thorax, the right lung and right 

 side of the heart, and from part of the convex surface of the liver. 



LYMPHATICS OF THE HEAD, FACE, AND NECK. 



The Lymphatic Glands of the Head (Fig. 395) are of small size, few in number, 

 and confined to its posterior region. They are the occipital and posterior 

 auricular. The occipital set are placed at the back of the head along the attach- 

 ment of the Occipito-frontalis muscle. The posterior auricular set are placed near 

 the upper end of the Sterno^mastoid muscle. Both these sets of glands are 

 affected in cutaneous eruptions and other diseases of the scalp. In the face the 

 superficial lymphatic glands are more numerous : they are the parotid, some of 

 which are superficial, and others deeply placed in the substance of the parotid 

 gland ; the zygomatic, situated under the zygoma ; the buccal, on the surface of the 

 Buccinator muscle ; and the internal maxillary, the largest, beneath the ramus of 

 the lower jaw. 



The lymphatic vessels of the scalp are divided into an anterior and a posterior 

 set, which follow the course of the temporal and occipital vessels. The temporal 

 set accompany the temporal artery in front of the ear, to the parotid lymphatic 

 glands, from which they proceed to the lymphatic glands of the neck. The 

 occipital set follow the course of the occipital artery, descend to the occipital 



