4GO ANATOMY OF VERTEBRATES. 



municating with the caudal vein. The three tunics of these 

 hearts, of which the middle one is muscular, with the inferent 

 and afferent valvular structures, are well displayed in the 

 Python. 1 



The intestinal lymphatics, in Serpents, open into a large 

 receptacle, extending along the root of the mesentery, beginning 

 near the vent where it is narrow, receiving the lymphatics of 

 the tail, and extending forward, greatly expanded, as far as the 

 stomach, where it forms a cul-de-sac. This receptacle is reflected 

 about the aorta, which seems included in it, and receives the 

 lymphatics of the genital organs, kidneys, and intestines. Before 

 reaching the stomach, it sends off a plexiform conduit, which 

 receives the lymphatics of the pancreas, spleen, stomach, and 

 liver, the latter gland being more or less completely sheathed by 

 the lymphatic receptacle ; this then contracts into an irregular 

 canal as it approaches the pericardium, where it terminates in a 

 cul-de-sac, but transmits the lymph by several lateral vessels to 

 a large plexus near the great vessels of the heart. The above 

 continuation of the abdominal receptacle has been called the 

 f right ' or ' inferior ' thoracic duct. The ' left ' or ' superior ' or 

 ' dorsal ' thoracic duct leaves the great receptacle nearer its 

 anterior extremity, by three or four conduits, and advances along 

 the oesophagus to the pericardium, anastomosing with the right 

 duct, by transverse channels. On reaching the pericardium, the 

 left duct divides into two channels, which reunite in front of 

 the pericardium, and join the lymphatic plexus about the great 

 vessels, from which the lymph is conducted by two or three 

 terminal trunks to the two great precaval veins. 2 



In Chdonia the chyle is absorbed into a stratum of intestinal 

 lymphatics, which, in the form of a close network, lies between 

 the muscular and mucous coats ; 3 from this the conduits pierce 

 the muscular tunic, and affect a longitudinal course on the 

 exterior of the gut until they quit it, accompanying the me- 

 senteric bloodvessels to the great chyle- and lymph-receptacle, 

 fig. 307, C, c, which extends from the middle of the dorsal part 

 of the abdomen backward to between the vertebras and rectum. 

 Here it receives the lymphatics of the hinder limbs and tail, and, 

 in succession forwards, those of the cloaca and its appendages, ib. 

 u, u, of the kidneys, ib. O, of the genital organs, ib. H, and intes- 

 tines, ib. v ; it presents the same quasi-capsular relation to the 



1 CCLX. p. 538, pi. 13, figs. 7, 8, 9. 2 CCLVII. p. 15. 



3 xx. vol. ii. p. 17, nos. 850-858. 



