302 



REPTILIA. 



gives origin to two thoracic ducts, or rather 

 to several principal trunks, which, as they 

 advance, form two complicated plexuses, ex- 

 tending as far as the subclavian veins on each 

 side, where they receive the lymphatics of 

 the head, neck, and anterior extremities. On 

 the right side, two branches pass from the 

 plexus to open into the jugular vein, near its 

 junction with the subclavian ; on the left side 

 there is only a single lymphatic trunk, which 

 opens into the jugular near the same point. 



Among the Saurian reptiles the arrange- 

 ment of the lymphatic system is as follows. 

 In the pike-headed Caiman, there is a sacral 

 plexus formed by the lymphatic vessels de- 

 rived from the tail, and the posterior ex- 

 tremities under the vertebra, which represents 

 the sacrum ; this plexus is continued along 

 the aorta and the vena cava, the former vessel 

 being in some places quite inclosed by it: 

 this forms the principal reservoir of the lym- 

 phatic system. Opposite the third and fourth 

 lumbar vertebrae, this reservoir receives the 

 anterior trunks derived from the lateral pelvic 

 plexuses, as well as those of the kidneys and 

 of the loins ; it then runs forward and slightly 

 to the left side, above the vena cava, where 

 it receives the lymphatics of the mesenteric 

 plexus. 



Arrived opposite the conjunction of the 

 two aortae, this reservoir divides into four 

 trunks, which represent the thoracic duct ; 

 these trunks unite and separate again several 

 times as they advance forward : at last they 

 form two fasciculi of vessels, which separate 

 to the right and left, and terminate in the 

 corresponding subclavian veins, having first 

 received the lymphatics derived from the 

 head and neck and anterior extremities. 



In the green Lizards, the central reservoir 

 of the lymphatics commences a little in front 

 of the anus, by a cul-de-sac, which receives 

 the lymphatics* of the hinder extremities, of 

 the kidneys, and of the rectum ; it then ad- 

 vances forwards in the abdomen, becoming 

 considerably dilated, and collects the lym- 

 phatics of the small intestines, and partly 

 those of the stomach. A little in front of 

 the latter viscus there is a constriction which 

 seems to indicate the limit between the reser- 

 voir and the thoracic duct. The latter vessel 

 runs between the oesophagus and the vertebral 

 column ; and afterwards between the latter 

 and the left lung. Arrived at the heart, it 

 divides into two diverging branches, which, 

 running outwards, terminate in the anterior 

 vena cava. 



In the Ophidian reptiles the central 

 lymphatic reservoir commences in front of 

 the anus, and advances forward inclosed 

 between the layers of the mesentery, be- 

 tween the intestines and the vertebral co- 

 lumn ; becoming much enlarged as it ad- 

 vances forwards, and ultimately terminating in 

 a conical cul-de-sac, opposite the commence- 

 ment of the stomach. This reservoir receives 

 the lymphatics from the tail, from the penis, 

 from the kidneys, the testicles, the intestine, 

 the stomach, and the dorsal region of the 



spine. A little before its termination in the 

 cul-de-sac it gives off several branches, which, 

 united into a single trunk, form the left 

 thoracic duct. This runs forward between 

 the stomach and liver, and subsequently 

 between the liver and the oesophagus, to 

 arrive at the region of the heart. The in- 

 ferior or anterior right thoracic duct com- 

 mences by a narrow cul-de-sac situated just 

 behind the pancreas, and receives the lym- 

 phatics of the pancreatic plexus, as well as 

 those from the spleen and gall-bladder. It 

 runs forward above the vena porta and the 

 vena cava ; between the layers of the epi- 

 ploon it receives three considerable branches 

 from the right thoracic duct, and most of the 

 lymphatics of the stomach ; it then expands 

 very considerably to envelope the stomach, 

 and becoming again contracted beyond that 

 viscus, it runs forward beneath the lung as far 

 as the right side of the heart, near the en- 

 trance of the vena cava, into the pericardium, 

 where it terminates by a cul-de-sac, after re- 

 ceiving several branches from the lungs. 



Three other considerable lymphatic trunks, 

 one mesial and inferior, the two others lateral, 

 run along the whole length of the body from 

 the head to the base of the heart, conveying 

 into the cardiac plexus the lymph from all 

 the anterior part of the body. 



The cardiac plexus, which is situated in 

 front of the base of the heart, is formed by the 

 confluence of all the lymphatic trunks, form- 

 ing as it were a central reservoir, being com- 

 posed, first, of the three anterior lymphatic 

 vessels mentioned above; secondly, by the 

 left thoracic duct ; and, thirdly, by a trunk 

 which combines the lymphatics of the lung and 

 the right thoracic duct. 



This reservoir opens into the anterior vena 

 cava. 



The lymphatic system of reptiles offers one 

 peculiarity of structure which is very remark- 

 able. Besides the usual termination of the 

 principal lymphatic trunks in the venae cavae 

 or in the axillary, subclavian, or jugular veins, 

 it has been discovered that some lymphatic 

 trunks open into small capsules which present 

 alternate movements of contraction and dila- 

 tation, and which propel the lymph that they 

 contain immediately into small contiguous 

 veins : these capsules are therefore lymphatic 

 hearts. 



Such lymphatic hearts have been found 

 to exist, both in the Saurian, Ophidian, and 

 Batrachian orders of reptiles, the Chelonians 

 only appearing to be without them. They 

 are generally situated near the posterior ex- 

 tremity of the body, and discharge into the 

 venous system the lymph derived from the 

 most remote parts. 



In the crocodile the lymphatic hearts are 

 found on each side lodged between the upper 

 border of the pelvis and the transverse process 

 of the first caudal vertebra. They resemble 

 elongated transparent bladders, and commu- 

 nicate with the veins of the kidney. 



In the green lizard they occupy a similar 

 situation, but they open into a vesicle thai" 



