THE LYMEHATIC VESSELS OF THE SEROUS MEMBRANES. 47 



These figures, together with their explanation, will undoubtedly 

 make these relations sufficiently clear. 



(c.) The Lymphatic Vessels of the Mesentery. 



The mesentery possesses, as it is known, two kinds of lymphatic 

 vessels ; first, vessels which run from the intestine to the roots of the 

 mesentery into the mesenteric glands ; and, secondly, vessels which 

 belong to the mesentery itself. The vessels of the first kind run in a 

 radiatory direction and are situated in the chief trabeculse of the 

 mesentery, together with the large blood-vessels, which run to and 

 from the intestine. These lymphatic vessels are distinguished by 

 their numerous valves and by their continuous rich ciicular muscular 

 coat. Their endothelium is spindle-shaped, like that in the lymphatic 

 trunks in general. The vessels of the second kind are : (a) large 

 lymphatic vessels, which accompany also, like those of the first kind, 

 the larger blood-vessels. They are either single or, generally, double : 

 in the former case the lymphatic is situated between the arterial and the 

 venous trunk ; in the latter the artery and the vein lie both between 

 the two lymphatics. They are anastomosing with each other by a few 

 wide branches. Here and there they possess a valve ; they have no 

 muscular coat ; their coat consists only of one layer of endothelium, 

 which is more or less elongated, spindle-shaped. In many places the 

 breadth of the endothelial cells is not much inferior to the longi- 

 tudinal diameter. The lymphatic vessels of this kind are very often 

 found to invaginate the arterious or venous trunk for a longer or 

 shorter distance, especially with their large sacciform dilatations. 

 These dilatation-sinuses are constantly to be found on the lymphatics 

 of mammals, as well as in those of frogs. Especially in rana tempo- 

 raria, and in bufo, I have come across not a few mesenteries 

 where, instead of lymphatic vessels which accompany the blood- 

 vessels, there was a system of lymph-sinuses, situated behind each 

 other and communicating with each other by small openings. This 

 depends very much upon the arrangement of the ground-substance, 

 for in these latter cases there were large trabeculao in which the 

 large blood-vessels and nerve-trunks were imbedded, from which 



