256 THE HEART, BY F. SCHWEIGGER-SEIDEL. 



It has already been mentioned that the smooth fissures are 

 covered with a delicate membrane analogous to the endothelium 

 of the lymphatics, to which it must also be added, that it is 

 easy to follow sub-pericardial lymph vessels and their prolonga- 

 tions into the lacunar system. That this system cannot be in- 

 jected through the vessels constitutes no objection to our view, 

 On sticking an injection pipe into the muscular substance of 

 the heart, the fluid penetrates between the several elements of 

 the muscles into the perimysium, and may become widely dif- 

 fused, so that with slight pressure we may even see the injec- 

 tion penetrating into the lymph vessels of the pericardium 

 without any evident rupture or extravasation. A complete 

 injection of the lacunse cannot be obtained in this manner. It is 

 observable that the lymphatics of the muscular substance are 

 not always in the form of fissures, but sometimes assume a 

 tubular form, dependent upon the amount of injection forced in, 

 and upon the degree of contraction of the muscular substance. 



In regard to the finer distribution of the cardiac nerves, 

 which is of peculiar physiological importance, little is at present 

 known, and our knowledge is particularly defective in reference 

 to the more intimate histological relations of the fibres spring- 

 ing from various sources and distributed to the different 

 tissues. 



The nerve fibres proceeding from the plexus cardiacus lie in 

 mammals beneath the pericardium, but in part also they are 

 found in the septum ventriculorum, where they run in the 

 substance of the muscular mass and in the spaces between the 

 two ventricles. Their distribution under the pericardium is 

 independent of the vessels, and it even appears in some animals 

 that the nerves cross the superficial muscular fasciculi and the 

 vessels at right angles, as is clearly shown in the illustrations 

 given by Lee * 



The isolated, somewhat flattened fibres, which intercommuni- 

 cate by means of delicate fasciculi, consist chiefly of non-medul- 

 lated nerve fibres. The double-contoured fibres vary in relative 

 proportion, but are usually only sparingly present. The nerves 



* R. Lee, Philosophical Transactions, London, 1849, Plates ii. and iii. 



