970 HUMAN ANATOMY. 



The vessels from the external intercostals are somewhat larger than those from 

 the internal muscles and have a backward direction, terminating in the intercostal 

 nodes. It is upon these stems that the lateral intercostal nodes are situated when 

 present. Anastomoses occur between the two sets of vessels, and the internal set 

 also receives communicating stems from the parietal layer of the pleura, while the 

 external one receives branches from the muscles which cover the thoracic wall, 

 although the principal path for these leads to the axillary nodes. 



The Diaphragm. — The lymphatics of the diaphragm form rich net-works upon 

 both its surfaces, that upon the peritoneal surface being especially well developed, and 

 numerous vessels traverse the substance of both the muscular tissue and the centrum 

 tendineum, uniting the net-work of the abdominal with that of the thoracic surface. 

 Upon the thoracic surface the net-work is exceedingly fine and close-meshed in the 

 region of the centrum tendineum, being most distinct in the regions of the lateral 

 leaflets. From this net-work branches pass outward parallel to the muscular 

 fibres to unite with a series of anastomosing stems whose general direction is forward. 

 Branches coming from the more peripheral portions of the diaphragm also empty into 

 these stems, which carry the lymph forward to the diaphragmatic nodes, whence it 

 passes to the anterior mediastinal nodes. From the net-works of the lateral leaflets 

 of the central tendon collecting stems are also directed backward and medially tow ards 

 the aortic opening, which they traverse to terminate in the upper coeliac nodes. 



It is to be observed that the nodes of the thoracic surface are for the most part 

 situated anteriorly, while the coeliac nodes, which may be regarded as the principal 

 nodes of the inferior surface, are located posteriorly. Both sets of nodes, however, 

 receive lymph from both surfaces of the diaphragm by means of the perforating 

 branches which connect the upper and the lower net-works. The lower net-work 

 is, furthermore, connected with the lymphatics of the more lateral portions of the 

 peritoneum and also with those of the liver (page 980), while the upper net-work 

 makes connections with the lymphatic vessels of the pleurae. These communications, 

 when considered in connection with the existence of the perforating branches, explain 

 the occurrence of pleuritis as a sequence of subphrenic abscess or of the latter as a 

 sequence o^ thoracic empyema. 



The Heart. — The lymphatics of the heart are arranged in two principal net- 

 works, one of which lies immediately beneath the endocardium, while the other is 

 upon the outer surface of the organ immediately beneath the visceral layer of the 

 pericardium. The endocardial net-work communicates with the superficial one by 

 branches which traverse the heart musculature, and the flow of lymph from the 

 endocardial net-work takes place only through these communicating branches. The 

 superficial net-work extends over the whole surface of the heart, the vessels of which 

 it is formed being well supplied with valves and arranged so as to form characteristic 

 quadrate or rhomboidal meshes. From the net-work longitudinal stems pass up- 

 ward towards the base of the heart, corresponding in a general way to the cardiac 

 veins. Upon the anterior surface three stems are to be found passing upward 

 along the anterior interventricular groove, parallel to the anterior cardiac vein, and, 

 on arriving at the auriculo-ventricular groove, they unite to form a single trunk. 

 With this another stem unites which has its origin in the net-work of the posterior 

 surface of the heart and ascends along the posterior inter\'cntricu]ar groove, 

 parallel with the posterior cardiac vein. On reaching the auriculo-ventricular groo\e 

 it bends round to the left and, encircling the .base of the left ventricle, unites with 

 the anterior vessels. The conjoined trunk so formed passes upward along the pos- 

 terior surface of the pulmonary aorta, perforates the parietal layer of the pericardium, 

 and terminates in one of the bronchial nodes. 



From the net-work over the right side of the right ventricle another longitudinal 

 stem arises and passes upward parallel to the right marginal vein, and, on reaching the 

 auriculo-ventricular groove, winds around to the right and so reaches the anterior 

 surface of the heart. It then ascends parallel with the anterior trunk, along the pos- 

 terior surface of the pulmonary aorta, and also terminates in one of the bronchial nodes. 



The Lungs. — The lymphatics of the lungs may be regarded as consisting of 

 two sets, deep and superficial. The deep set is composed of a number of sterns 

 which accompany the branches of the pulmonary arteries and veins and of others 



