QUARTERLY CHRONICLE OF MICROSCOPICAL SCIENCE. 411 



send fortli processes which project between the endothelium 

 of the free surface, forming pseudostomata. 



Sub-pleural Lymphatics. — The pleural lymphatic sinuses 

 communicate with lymphatic tubes lying in grooves cor- 

 responding to the most superficial groups of the alveoli of the 

 lung. These vessels have valves, and anastomose to form a 

 network, which receives branches originating between the 

 alveoli of the superficial portions of the lung. These inter- 

 alveolar lymphatics commence in thelymph-canalicular system 

 of the alveolar septa, whose cells are in direct continuity with 

 the endothelium of the lymphatics. 



Perivascular Lym-phatics . — These originate also from 

 branched cells in the alveolar septa, the capillaries being 

 collected into trunks which accompany the branches of the 

 pulmonary artery and veins. They either run in the adven- 

 titia of these vessels in twos or threes, anastomosing with 

 each other, or the blood-vessel is entirely or partially invagi- 

 nated in a lymphatic. The branched cells of the alveolar 

 septa, from which the capillaries of this system originate, 

 send processes between the epithelium into the cavities of 

 the alveoli, thus forming pseudostomata. This is the only 

 ineans of communication between the alveolar cavities and 

 the lymphatics. 



Peribronchial Lymphatics. — These vessels are usually 

 distributed in the adveutitia of the bronchi, anastomosing 

 with each other and with the perivascular lymphatics. Their 

 capillaries originate in the mucous membrane of the bronchi 

 and pierce the muscular coat. The wall of these capillary 

 branches is continuous with the branched cells of the mucosa, 

 which also penetrate, as a nucleated reticulum, between the 

 epithelium of the bronchus and project on its free surface, 

 forming pseudostomata. The lymphatics are always most 

 numerous on that side of a bronchus which is turned towards a 

 branch of the pulmonary artery. In the course of the smaller 

 bronchi, whose walls have no cartilage, there are generally 

 several vascular lymphatic follicles, which are surrounded by 

 a lymphatic vessel, as the lymph-follicles of Peyer's patches 

 are by their lymph-sinuses. These follicles extend to the 

 muscular coat, and in some cases may be traced through it 

 to the mucosa. These follicles always lie in the wall of a 

 lymphatic vessel, between the bronchus and the accompa- 

 nying branch of the pulmonary artery. They are of difierent 

 sizes, and generally spherical or elliptical. These peri- 

 lymphangial follicles are especially numerous in the guinea- 

 pig's lungs, and are constantly growing and being repro- 

 duced. The lymphatic vessels of the two last-mentioned 



