190 LYMPHATIC SYSTEM. 



cubical cells, and the larger flattened epithelioid cells of the 

 serous membrane are arranged in a somewhat radiated manner in the 

 neighbourhood of the orifice. When the lymphatic is superficial, it 

 may communicate directly with the surface of the membrane ; in other 

 cases a short straight canal, lined with cells similar to those bounding 

 the orifice, leads from the vessel to the surface. A curious fact has 

 been pointed out by the same observer, viz., that in female frogs and 

 toads the cells lining these short lymphatic canals are furnished with 

 vibratile cilia. 



Termination. — The absorbent system discharges its contents into 

 the veins at two points, namely, at the junction of the subclavian and 

 internal jugular veins of the left side by the thoracic duct, and at 

 the corresponding part of the veins of the right side by the right 

 lymphatic trunk. The openings, as already remarked, are guarded 

 by valves. It sometimes happens that the thoracic duct divides, near 

 its termination, into two or three short branches, which open separately, 

 but near each other ; more rarely, a branch opens into the vena 

 azygos — indeed the main vessel has been seen terminating in that 

 vein. Again it is not uncommon for larger branches, which usually 

 join the thoracic duct, to open independently in the vicinity of the 

 main termination ; and this is more apt to happen with the branches 

 which usually unite to form the right lymphatic trunk. By such 

 variations the terminations in the great veins are multiplied, but still 

 they are confined in man to the region of the neck ; in birds, reptiles, 

 and fish, on the other hand, communications take place between the 

 lymphatics of the pelvis, posterior extremities and tail, and the sciatic 

 or other considerable veins of the abdomen or pelvis. 



The alleged terminations of lymphatics in various veins of the abdomen, de- 

 scribed by Lippi as occm-ring- in man and mammalia, have not been met with by 

 those who have since been most engaged in the prosecution of this department 

 of anatomical research, and accordingly his observations have generally been 

 either rejected as erroneous, or held to refer to deviations from the normal 

 condition. Nuhn, of Heidelberg, affirms the regular existence of these abdo- 

 minal terminations, and refers to three instances which he met with himself. 

 In two of these the Ijnnphatics opened into the renal veins, and in the other 

 into the vena cava.* 



Lymphatic hearts. — Miiller and Panizza. nearly about the same time, but in- 

 dependenth^ of each other, discovered that the lymphatic system of I'cptiles is 

 fva'nished, at its principal terminations in the venous system, with pulsatile 

 muscular sacs, which serve to discharge the lymph into the veins. These organs, 

 which are named Ijani^h-hearts, have now been found in all the different orders 

 of reptiles. In frogs and toads two pau-s have been discovered, a ijosterior 

 pair, situated in the sciatic region, which pour their hanph into a branch of the 

 sciatic or of some other neighbouring vein, and an anterior more deeply-seated 

 pair, placed over the transverse process of the third vertebra, and opening into 

 a branch of the jugular vein. The parietes of these sacs are thin and trans- 

 parent, but contain muscular tissue, which here and there appears obscurely 

 striated, decussating in different layers, as in the blood-heart. In their pulsations 

 they are quite independent of the latter organ, and are not even synchronous 

 with each other. In salamanders, lizards, serpents, tortoises, and turtles, only 

 a posterior pair have been discovered, which, however, agree in all essential points 

 with those of the frog. In the goose, and in other species of birds belonging 

 to different orders, Panizza discovered a pair of l^anph-sacs opening into the 

 iracral veins, and Stannius has since found that these sacs have striated muscular 



* Miiller's Archiv,'lSi8, p. 173. 



