102 



NORMAL HISTOLOGY. 



IG. 126. 



The muscular tissue of the heart possesses the peculiarities 

 already described in Chapter IV. : it is composed of short, branched, 

 nucleated fibre-cells, devoid of a sarcolemma, which unite to form 

 an intricate net-work. The naked niuscle-fibres are enveloped 

 within a ^ej.im.ysium and are grouped into primary and secondary 

 bundles, which are associated to form lamellae disposed in a very 

 irregular and complex manner. 



The muscular tissue of the auricles is arranged in general as an 

 outer transverse and an inner longitudinal layer, many small ad- 

 ditional bundles deviating from the principal disposition to pursue 



independent courses in various directions. 

 The muscle-bundles of the ventricles have 

 a very intricate arrangement, the majority 

 extending in an irregular oblique or spiral 

 direction, some, in fact, describing a figure- 

 of-eight in their course. 



The pericardium, which invests the 

 exterior of the heart, and by reflection 

 forms the pericardial sac, resembles the 

 endocardium in possessing a single layer 

 of endothelial plates covering its free 

 surface, and a stratum of fibre-elastic con- 

 nective tissue beneath. The parietal 

 pericardium is distinctly thicker than the 

 visceral, all the constituent layers being 

 better developed. The subpericardial 

 tissue covering the heart is continuous 

 with the intermuscular connective tissue 

 of the outer muscular layer ; in this posi- 

 tion numerous fat-cells lie between the 

 bundles of the fibrous and the muscular 

 tissue. 



The blood-vessels supplying the muscle 

 of the heart are derived as branches of 

 The principal trunks are situated in the 



larger interlamellar masses of connective tissue, within which they 

 divide into numerous twigs giving origin to the capillaries ; the 

 latter penetrate the primary muscle-bundles, among and parallel to 

 which they run. The relation between the individual muscle-fibres 

 and the capillaries is more intimate than usually supposed, since, as 

 shown by Meigs, the^lood-vessels deeply impress the fibres, and 

 in some places are surrounded completely by the muscular tissue. 

 The extraordinary demands made upon the nutrition of the heart- 

 tissue as the result of its remarkable functional activity explain the 



Section of human heart, including 

 pericardium : a, endothelium of 

 pericardial surface ; b, subendo- 

 thelial fibrous tissue ; c, net-works 

 of elastic fibres ; d, subpericardial 

 areolar tissue containing fat-cells 

 embedded between pericardium and 

 muscle (e) ; v, blood-vessel. 



the 



coronary 



arteries. 



