VASCULAR SYSTEM OF FISHES. 247 



system.' This system exists as a separate organic vascular apparatus 

 only in the Vertebrate subkingdom : it was first observed in Man and 

 Mammalia ; was discovered by John Hunter in Birds* and Eeptile.s|, 

 and afterwards described by JMi*. 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 

 Hevv'son. J 



The lacteal system in Fishes commences by a reticulate or plexi- 

 form layer of vessels attached to the cellular side of the mucous coat 

 of the stomach and intestines : in the Skate § the network is so coarse 

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

 cellular 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 receptacles, 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 corresponding differences in their 

 lacteal systems : in the Myxinoids the lacteals are supported and con- 

 veyed 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 forwai'ds, and enter the abdominal cavernous sinus be- 

 neath the aorta. 



The lymjihatic system is best demonstrated by injecting the large 

 absorbent trunk which runs upon the inner surface of the ventral 

 parietes of the abdomen, along the median line from the vent for- 



* " It is but doing justice to the ingenious Mr. John Hunter to nientiou here, 

 that these lymphatics in the necks of fowls were first discovered by him many 

 years ago." (Hewson, cii. 1768, p. 220.) 



f Hunter's account of this discovery, in a manuscript copied by INIr. Clift, is as 

 follows : — " In the beginning of the winter 17G4-5, I got a crocodile, which had 

 been in a show for several years in I^ondon before it died. It was, at the time of 

 its death, perhaps the largest ever seen in tliis country, liaving grown, to my know- 

 ledge, 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 Iiim my former de- 

 scriptions 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 ajjpcarances in the animal now before us ; 

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

 whicli Mr. Hewson took his observations of the colour of the chyle." Hunter liere 

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

 Amphibious Animals," Pliilosoiihical Transactions, vol. lix. 1769, p. 199. a : " In 

 a crocodile whicli I lately saw i>y favour of Mr. John Hunter, the chyle was 

 white." 



i CII. 1768, 1769. 



§ In this and other I'lagiostomcs the gastric lacteals are confined chiefly to the 

 contracted jiyloric canal. 



B 4 



