VOL. LVIII.] PHILOSOPHICAL TRANSACTIONS. 55Q 



that one part of it opened immediately into the vein, and the other joined the 

 thoracic duct of that side ; while on the left side, the vessel which issued from the 

 gland wholly joined the thoracic duct. In all the 4 subjects he evidently saw that 

 the thoracic ducts open into the inside of the jugular veins. 

 , This system in birds differs most from that in quadrupeds in the following 

 particulars. 1st. In the chyle being transparent and colourless. 2dly. In there 

 being no visible lymphatic glands, neither in the course of the lacteals, nor in 

 that of the lymphatics of the abdomen, nor near the thoracic ducts. 3dly. In 

 the several parts of this system in birds being more frequently enlarged, or vari- 

 cose, than in quadrupeds. In particular, this appears to be the case of the 

 vessels which constitute the network, at the root of the coeliac artery in that sub- 

 ject from which the drawing was taken. The lacteals are frequently enlarged in 

 some places ; so are the thoracic ducts ; and the lymphatics on each side of the 

 neck are commonly, when taken together, larger than their trunk which opens 

 into the lymphatic gland. In one subject, where instead of 2 lymphatics on the 

 left side, he found only one, that vessel was as large as a crow quill ; while the 

 lower part of it, which entered the gland, was much smaller. Thus far the 

 account of what he saw : he next begs leave to observe, that, as the supposed 

 want of this system in birds has been considered as a strong argument in favour 

 of absorption by the common veins, now, since we find it not wanting, that 

 theory must be much weakened. And he further adds, that absorption seems 

 to be carried on in birds, as in quadrupeds, by this system, at least principally; 

 indeed he was inclined to believe, entirely ; for no arguments brought in favour 

 of absorption by the common veins appeared to him of equal validity with those 

 that can be urged against it. The contrary opinion is indeed embraced by the 

 most learned and acute physiologist of the present age, who, treating of this 

 subject, expresses himself in the following manner : " it is a strong argument in 

 favour of absorption by the common veins, that neither birds, amphibious 

 animals, nor fish with cold blood, iiave either the lacteal or the lymphatic 

 system. Nature commonly observes a pretty strict analogy in her works, and 

 makes use of similar organs to jjerform similar functions. Now in all animals, 

 quadruj^eds and the whale excepted, we must admit of absorption by the 

 mesenteric veins, if in those animals there is no other way for the chyle to get 

 into the blood. And if those veins in birds and amphibious animals absorb the 

 chyle, it is very probable they likewise absorb it in quadrupeds, in which they 

 equally exist." But the existence of this system in birds is not the only fact 

 which might be adduced to invalidate the above opinion ; for he had seen a part 

 of it very distinctly in one of the amphibia, viz. the turtle.* Whether it is to 



• The part of this system, which he saw in the turtle, was the lacteals. He filled them with 

 quicksilver as far as the root of the mesentery, where they formed a considerable net-work into 

 which a lymphatic of the spleen entered. He had not an opportunity of tracing them farther, having 



