THE ENDOCARDIUM. 



373 



the fibres of the myocardium. In it run the vessels and nerves before dipping down 

 into the muscular substance, and a system of lymphatic vessels, connected with the 

 lymphatic spaces of the myocardium, also occurs here. The vessels and nerves are 

 generally imbedded in a considerable amount of fat (fig. 325, e), which is espe- 



Fig. 325. SECTION OF A PART OF THE PERICARDIUM 



OF THE RIGHT AURICLE. (E. A. S.) 



ct, serous epithelium in section ; b, connective 

 tissue layer ; c, elastic network ; d, subserous areo- 

 lar tissue ; c, fat ; /, section of a blood-vessel ; g, a 

 small ganglion ; h, muscular fibres of the myocar- 

 dium ; i, intermuscular areolar tissue. 



cially collected in the furrows, but may 

 in fiit subjects extend as a layer cover- 

 ing the greater part of the surface, and 

 may even be found in the larger inter- 

 spaces of the myocardium, and beneath 

 the endocardium. 



ENDOCARDIUM. 



The endocardium furnishes a lining to all the cavities of the heart, following 

 the inequalities of the inner surface of the organ, and becoming continuous at the 

 venous and arterial orifices with the inner coat of the respective veins and arteries. 

 A layer of endothelial cells covers and lines the inner surface (fig. 326, a), and 



Fig. 326. SECTION OF A PART OF THE ENDOCARDIUM OF 



THE RIGHT AURICLE. (E. A. S.) 



a, lining epithelium ; b, connective tissue with fine elastic 

 fibres ; c, layer with coarser elastic fibres ; d, subendocardial 

 connective tissue continuous with the intermuscular tissue of 

 the myocardium ; h, muscular fibres of the myocardium ; ra, 

 plain muscular tissue in the endocardium. 



beneath this the endocardium consists of connective tissue with a close network of 

 elastic fibres often passing into fenestrated membrane. Plain muscular fibres are 

 present in some parts (m). The ordinary cardiac muscular fibres extend in many 

 places close up to the endocardium, but in others are separated from it by some 



Fig. 327. FRAGMENT OF THE NET- 

 WORK OF PURKIJSJE FROM THE 

 VENTRICULAR ENDOCARDIUM OF 



THE SHEEP. (Ranvier.) 3 s. 



c, cell ; /, striated substance ; 

 n } nuclei. 



amount of areolar tissue. In 



this tissue, fat is often met 



with, especially in fat subjects 



and in fatted animals. In the 



ventricles of some animals, as 



the horse and sheep, large beaded reticulating fibres are met with lying in the subendo- 



cardial tissue and, having been first described by Purkinje, are known by his name. 



When examined with the microscope these fibres of Purkinje are found to be composed 



of large clear cells, joined end to end, and containing in their centre one or two nuclei 



B B 2 



