250 STRUCTURE OF THE 



that the appearance of large cells (cxix*) may be a deception, 

 from the circumstance I have already mentioned ; and I am the 

 more confirmed in my opinion that this is the case, on taking 

 a more general survey of this subject in the animal kingdom, 

 as in the turtle, where the lymphatic glands are wanting, or 

 at least that circumscribed form of a lymphatic gland, so ge- 

 neral in the more perfect animals, is not to be found in those 

 of the amphibious class. 



SECT. 13. In the mesentery of a turtle no lymphatic glands 

 are observable; yet in this animal nature does her business as 

 well, though the apparatus is differently constructed. The 

 small blood-vessels in the mesentery of this animal are trans- 

 parent in an unprepared state, and the large vessels form a 

 network, making seemingly pretty considerable meshes, but if 

 we inject them (i. e. the veins and arteries) we find this part 

 exceedingly vascular, and from its transparency we can here 

 prove the artery terminating in the vein by continuity of canal 

 (a fact not easy to demonstrate in the human body) ; and if we 

 inject the lymphatic vessels, we find them very numerous, form- 

 ing the most beautiful network imaginable. 



The lacteals come from the edge of the intestines upon the 

 mesentery ; part of them ascend, surrounding the blood-vessels, 

 but do not communicate with them. These send off lateral 

 branches to the transparent part of the mesentery, whilst others 

 come immediately from the intestines to it, where they divide 

 to exceeding minuteness, making frequent anastomoses, and 

 gradually becoming larger as they approach the upper angle, 

 where they communicate with the larger branches, and pass on 

 to the thoracic duct. Vide Plate VII. 



SECT. 14. The arteries and veins are principally spread on 



(cxix*.) Mr. Abernethy a found the mesenteric glands of a whale 

 hollow in the centre, like a bag'. Mr. John Goodsir b concludes that 

 the lymphatic glands are merely networks of lymphatic vessels, deprived 

 of all their tunics but the internal, the epithelium of which is highly 

 developed for the performance of particular functions ; and that these 

 peculiar lymphatics have a fine network of capillary blood-vessels to 

 supply matter for the continual renovation of the epithelium. He states 

 that the outer tunic of the extra-glandular lymphatics leaves them at 

 their entrance to or exit from the gland, and passes on its surface to 

 form its capsule. 



a Philosophical Transactions, 1796, pp. 27 b Anatomical and Pathol. Observations, 

 et seq. pp. 45, 49, 8vo, Edin. 1845. 



