456 MANUAL OF HISTOLOGY. 



Fig. 437, after an old drawing, represents the original cells in the 

 meshes of the capillary network of a young animal. 



The condition of parts, on the other hand, in the mature mammal, is 

 given in hg. 438. Here large non-nucleated plates are seen, with remnants 

 of the original small cells, and a trace of the protoplasm and nucleus with 

 them, at their points of contact and corners (Schulze). 



The nerves of the organs of respiration spring from the anterior 

 and posterior pulmonary plexus. They are derived partly from the sym- 

 pathetic and partly from the vagus, and take the same course, to a great 

 extent, as the ramifications of the bronchi or the pulmonary arteries. 



Fig. 438. Epithelium from the base of an infundibulum situated immediately under 

 the pleura. From a fully-grown cat ; treated with nitrate of silver. 



The pulmonary veins and bronchial arteries are not accompanied to the 

 same extent by nervous twigs. On the external surface of the bronchi 

 there are to be found, in connection with the latter, numerous small ganglia 

 (Remak). The same are seen on the finer ramifications of the nerves in 

 the tissue of the lung (ScJiiff). These nervous filaments appear to ter- 

 minate in many cases in the mucous membrane of the bronchi. 



The pleural covering of the lung and thorax presents, as far as epithe- 

 lium and connective-tissue substances are concerned, the ordinary texture 

 of all serous membranes. The nerves of the structure are derived from 

 the phrenic, vagus, and sympathetic (plexus pulmonalis). Those distri- 

 buted to the pulmonary pleura are stated by Koelliker to have scattered 

 ganglion cells among them. The vascularity of the membrane is low, 

 the capillaries being very fine, and forming wide meshes. The pulmonary 

 pleura receives its vessels, as has been already mentioned, from the pul- 

 monary and bronchial arteries. 



The lymphatics of this membrane are to some extent well known, espe- 

 cially from the recent studies of Dyblcowsky. In the dog they are only 

 evident in the movable portions of the parietal layer, i.e., in the inter- 

 costal spaces, and upon the sterna costalis muscles, but not upon the ribs. 

 On the mediastinal portion they are only seen at those spots where col- 

 lections of fat-cells exist. 



