4o() ANATOMY OF VERTEBRATES. 



Birds l and Reptiles, 2 and afterwards described by Mr. Hewson 

 and Dr. Monro in Fishes. The most systematic and detailed 

 descriptions of the absorbent system of the Oviparous Animals, 

 published in the last century, are those of Hewson. 3 



§ 79. Absorbents of Fishes. — The lacteal system in Fishes 

 commences by a reticulate or plexiform layer of vessels attached 

 to the connective tissue on the outer or cellular side of the mucous 

 coat of the stomach and intestines : in the Skate 4 the network is so 

 coarse that, when inflated, dried, and cut open, it appears like a 

 subdivided cellular or areolar receptacle. The chyle is conveyed 

 thence in all Fishes by more vasiform lacteals, situated immediately 

 beneath the serous covering of the intestines, to large reticulate re- 

 ceptacles, one in the mesenteric angle along the junction of the small 

 and large intestines, the other extending along the duodenum, its 

 pancreatic appendages, and the pyloric part of the stomach, and 

 often also surrounding the spleen. The presence of the mesentery 

 in the Myxinoids, and its absence in the Lampreys, involve corre- 

 sponding differences in their lacteal systems: in the Myxinoids 

 the lacteals are supported and conveyed by the mesentery to the 

 dorsal region of the abdomen, and empty themselves into a 

 receptacle above the aorta and the cardinal veins, between these 

 and the vertebral chord : in the Lamprey the lacteals pass 

 forward, and enter the abdominal cavernous sinus beneath the 

 aorta. 



The lymphatic system is best demonstrated by injecting the 

 large absorbent trunk which runs upon the inner surface of the 



1 ' It is but doing justice to the ingenious Mr. John Hunter to mention here, that 

 these lymphatics in the necks of fowls were first discovered by him many years ago.' 

 (Hewson, civ. 1768, p. 220.) 



2 Hunter's account of this discovery is as follows: — ' In the beginning of the winter 

 1764-5, I got a crocodile, which had been in a show for several years in London 

 before it died. It was, at the time of its death, perhaps the largest ever seen in this 

 country, having grown, to my knowledge, above three feet in length, and was above 

 five feet long when it died. I sent to Mr. Hewson, and, before I opened it, I read over 

 to him my former descriptions of the dissections of this animal relative to the 'absorbing 

 system,' both of some of the larger lymphatics and of the lacteals, with a view to see 

 how far these descriptions would agree with the appearances in the animal now before 

 us; and, on comparing them, they exactly corresponded. This was the crocodile 

 from which Mr. Hewson took his observations of the colour of the chyle.' Hunter 

 here alludes to the note appended to Mr. Hewson's paper on the ' Lymphatic System 

 in Amphibious Animals,' Philosophical Transactions, vol. lix. 1769, p. 199 a- 'In 

 a crocodile which I lately saw by favour of Mr. John Hunter, the chyle was 

 white.' 



3 civ. 1768, 1769. 



* In this and other Plagiostomes the gastric lacteals are confined chiefly to the 

 contracted pyloric canal. 



