488 SEROUS CAVITIES. [BOOK n. 



manner ; the whole arrangement serves as a communication from 

 the peritoneal cavity into the cisterna, and by these stomata the 

 peritoneal fluid passes into the cisterna and so into the general 

 lymphatic system. Owing to causes which we shall study presently 

 the contents of the small lymphatic vessels and such spaces as the 

 cisterna are continually being drained by the vascular system ; the 

 cisterna is continually tending to empty itself and so to draw fluid 

 from the peritoneal cavity through the stomata. In the female 

 frog the small granular cells encircling the stomata are, during the 

 breeding season provided with cilia, the action of which increases the 

 current from the peritoneum through the stoma into the cisterna. 



In the mammal similar stomata place the serous cavities in 

 connection with the lymphatics of the walls of those cavities. 

 They may be readily seen in the tendon of the diaphragm. 

 The peritoneal membrane of the mammal as of the frog consists 

 of a single layer of flat epithelioid plates lying on a connective- 

 tissue basis; the plates, smaller than those in the frog, are polygonal 

 in form, and their outline is not sinuous. On the tendon of the 

 diaphragm the epithelioid plates over the radiating spaces, or 

 clefts between the radiating bundles of the tendon, are smaller than 

 over the bundles themselves, and along the lines of these radi- 

 ating intertendinous spaces may be seen stomata, orifices guarded 

 by small cells, similar to but smaller than and less conspicuous 

 than those just described as seen in the frog. These stomata 

 open into the lymphatics which are abundant in the connective 

 tissue lying between the radiating bundles of the tendon of the 

 diaphragm, and through them the fluid of the peritoneal cavity 

 passes away into the lymphatics of the diaphragm and so into the 

 general lymphatic system. The movements of the diaphragm in 

 breathing, of which we shall have to speak presently, greatly assist 

 the flow through the stomata ; and even passive movements of 

 the diaphragm are effectual for this purpose. If a quantity of 

 injection material, such as a solution of Berlin blue, be injected 

 into the peritoneal cavity of a living animal it soon enters into and 

 injects the lymphatics of the diaphragm, and a similar injection 

 may be obtained in a dead but recently killed animal by placing 

 the animal with its head downwards, injecting the colouring 

 matter into the abdomen, or even pouring it into the hollow of 

 the diaphragm, and then producing movements of the diaphragm 

 by a rhythmically repeated artificial respiration. Not only 

 coloured fluids but coloured material merely suspended in fluid 

 and such things as the globules of fat in milk, or even red blood 

 corpuscles may thus find their way from the peritoneal cavity into 

 the lymphatics of the diaphragm. Indeed if a piece of the 

 diaphragm of a recently killed animal be stretched out and milk 

 poured upon it, the fat globules of milk may be seen with the aid 

 of a lens or microscope to disappear through the stomata in a 

 number of minute vortices. 



