THE LYMPHATICS OF THE HEAD. . 945 



lymphatic vessels offer little obstacle to free transudation, which, when it follows 

 obstruction, may be compared to the hematemesis seen in hepatic cirrhosis (RoUeston). 



The symptoms of obstruction are neither so constant nor so marked as they 

 would be if it were not that (a) the lymphatic system is not, like the veins, a series of 

 closed vessels, but is practically continuous with the interstices of the tissues ; and that 

 (d) it communicates with the venous system, the duct itself with the azygos vein in the 

 posterior mediastinum, and the smaller lymphatics with venules elsewhere — certainly, 

 for example, in the inguinal region, and probably in other parts of the body (Leaf ). 



The effects of obstruction are most often noticeable when the interference with 

 the flow of lymph takes place near the ternTination of the duct on the outer side of 

 the internal jugular vein, near its junction with the subclavian. This is probably 

 due to (a) the frequency of tumor or of injury in this situation ; (d) the consolida- 

 tion of the lymph-vessels here into a single trunk ; (<:) the greater difficulty in estab- 

 lishing a compensatory collateral circulation between the parts of the duct above and 

 below the obstruction than if the latter were lower down (Rolleston). 



Chylous ascites may be due either to obstruction with transudation of chyle 

 from distended lacteals into the peritoneal cavity, or to wound or rupture of the 

 thoracic duct, or of the larger lymph-vessels, or of varicose lymph-vessels, or of 

 lymphangiomata. Chylous pleural effusions may similarly result, or an effusion fol- 

 lowing wound or rupture may be partly thoracic and partly abdominal, as in a case 

 in which, after extreme compression of the chest, death followed in three weeks, and 

 the thoracic duct was found ruptured where it traversed the hiatus aorticus (Bellamy). 



When the receptaculum chyli is involved, the thoracic duct above may be quite 

 healthy, and lymph may pass into it by anastomotic channels and no chylous ascites 

 be produced. 



Carcinoma of the aortic or mesenteric nodes may cause enough dilatation of the 

 lymphatics to bring about chylous ascites. 



THE RIGHT LYMPHATIC DUCT. 



The right lymphatic duct (ductus lymphaticus dexter) (Fig. 795) opens into the 

 right subclavian vein and is a very short -stem, rarely having a length of more than 

 from 10-12 mm. It is formed by the union of the right jugular and subclavian 

 lymphatic trunks, the right broncho-mediastinal trunk rarely contributing to its 

 formation, but ha\ing usually an independent opening into the subclavian vein. 

 Very frequently no right lymphatic duct exists, the jugular and subclavian trunks, 

 as well as the broncho-mediastinal, opening independently into the vein. 



THE LYMPHATICS OF THE HEAD. 

 The Lymph-Nodes. 



The lymphatic nodes of the head are arranged in groups, which, for the most 

 part, are situated along the Hne of junction of the head and neck regions, that is to 

 say, along a line extending from the external occipital protuberance to the temporo- 

 mandibular articulation and thence along the rami of the mandible. A few small nodes 

 also occur upon the cheeks, and others which lie upon the surfaces of the hyo-glossus 

 and genio-hyo-glossus muscles and upon the upper part of the posterior surface of 

 the pharynx may be regarded as belonging to the head region. Including these, 

 the various groups recognizable in the region are (i) the occipital, (2) the posterior 

 auricular, (3) the anterior auricular, (4) ihe parotid, (5) the submaxillary, (6) the 

 submental, (7) \\-\e facial, (8) the lingual, and (9) the retropharyngeal ^xowi^%. 



The occipital nodes (lyniphoglandulae occipitales) are from one to three in num- 

 ber and are situated at the base of the occipital triangle, immediately lateral to the 

 border of the trapezius muscle and resting upon the upper part of the semispinalis 

 capitis (Fig. 796). Their afferents come. from the occipital portion of the scalp and 

 their efferents pass to the upper nodes of the superior deep cervical group. 



The posterior auricular or mastoid nodes (lymphoglandulae auriculares 

 posteriores) are usually two in number and are of small size ; they rest upon the 

 mastoid portion of the insertion of the sterno-cleido-mastoid muscle (Fig. 796). 



60 



