4i0 QUARTERLY CHRONICLE OF MICROSCOPICAL SCIENCE. 



enclosed in a tube of protoplasm, the nucleus bein;^ closely 

 applied to the side of the fibre ; or it may be thin and flattened 

 and spread out in one of the meshes of the reticulum, which 

 it occupies as a picture does its frame ; the nucleus then 

 occupies the centre of the mesh. A similar arrangement 

 holds good in the other animals examined. 



Bizzozero affirms that in the reticulum of the follicular 

 cylinders the same relations may be seen. The reticulum 

 here consists of delicate, homogeneous, communicating fibres, 

 flattened and broad at the nodular points. It is on, and not 

 in, these nodular points that the cells lie. They consist of 

 an oval nucleus with a very narrow protoplasmic zone, and 

 can also be dislodged by prolonged shaking, without injury 

 to the reticulum. 



Bizzozero has also succeeded in demonstrating the exist- 

 ence of a layer of endothelium covering the follicular 

 cylinders, and thus forming the wall of the lymph-paths. 



8. Normal and Pathological Anatomy of the Lymphatic 

 System of the Lungs. — Klein (' Proc. E,oy. Soc.,' 1874, No. 

 149) gives a full description of the above, as seen in guinea- 

 pigs, dogs, cats, rats, and rabbits. The endothelium of the 

 surface of the pulmonary pleura consists of a single layer of 

 polyhedral cells, which are not flattened, but shortly columnar 

 and granular, that of the costal pleura being formed of much 

 flattened, almost hyaline plates. The pulmonary pleura 

 consists of a thin layer of connective tissue, with a very rich 

 network of elastic fibres, the matrix usually contains one 

 layer of flattened connective-tissue-corpuscles. Beneath the 

 pleura, in the guinea-pig, there is a membrane consisting of 

 unstriped muscle, arranged in bundles so as to form a mesh- 

 work, with elongated large meshes, which have a greater 

 diameter in the distended than in the collapsed lung. These 

 muscular bundles radiate from the apex to the base of the 

 lung, and are most abundant on the anterior external and 

 internal surfaces ; on the posterior surface they are scanty, 

 and become more and more so near the spinal column, the 

 fibres being most richly distributed over those parts of the 

 lung which move most actively in respiration. In rats, 

 rabbits, cats, and dogs, the muscular bundles occur more 

 sparingly. 



Pleural Lymphatics. — The meshes of the muscular mem- 

 brane in the guinea-pig's lung are lined by a single layer of 

 flattened endothelium, and constitute a communicating system 

 of lymphatic sinuses, which communicate freely by true 

 stomata with the pleural cavity. The cells of the membrana 

 propria of the pulmonary pleura (lymph-canalicular system) 



