CIRCULATING SYSTEM. 335 



tines, in the form of extremely minute radicles, which unit- 

 ing, form the trunks in the coats of the intestines. These 

 trunks afterwards pass through the mesentery, occasionally 

 become much convoluted, and form glands, liberally sup- 

 plied with bloodvessels, and ultimately terminate in the 

 Thoracic Duct. This duct, the commencement of whicli 

 is usually termed Receptacidum Chyli, has slender walls, 

 and internal valves, and empties its contents into the sub- 

 clavian vein. In many quadrupeds, birds, and reptiles, 

 there are two ducts, one on each side ; but neither the size 

 nor proportion of the parts appear uniform, especially in 

 domesticated animals. 



With regard to the nature of the chyle itself, little satis- 

 factory information has been obtained. When procured 

 from the thoracic duct of quadrupeds, and allowed to rest, 

 a coagulum speedily separates, which has been compared 

 to fibrin, and the serous fluid which remains contains a con- 

 siderable proportion of coagulable albumen. When the num- 

 ber of secreted fluids which are mixed with the food pre- 

 vious to the separation of the chyle is considered, we need 

 not be surprised at the near approach which it makes in 

 composition to the blood, into which it is about to be chan- 

 ged. But does it undergo no change from its entrance into 

 the lacteal s, at the villous surface of the intestine, until it is 

 poured into the thoracic duct ? 



Many physiologists are disposed to consider the mesen- 

 teric glands as destined to effect some change in the nature 

 of the chyle, during the passage of the lacteals through 

 them. This opinion has been supposed to receive consi- 

 derable support from the observations of Mr ABERNETHY 

 " on some particulars in the Anatomy of a Whale *." He 

 found the mesenteric glands forming bags, on the inner 



Phil. Trans, vol. Ixxxvi, p. 27. 



