MICROSCOPICAL STRUCTURE OF THE MYOCARDIUM. 



371 



the most gradual transition into the diagonal ones nearer the surfaces, so that any 

 separation into layers which may be effected (with the exception of the superficial 

 stratum over the right ventricle) must be looked upon as in a great degree artificial. 

 Microscopical structure of the myocardium. The muscular fibres of the 

 heart are cross-striated, but differ from the fibres of the voluntary muscles in being 



Fig. 323. VIEW OF A PARTIAL DISSECTION OF THE 

 FIBRES OF THE ANTERIOR WALL OF THE VENTRICLES 

 IN A SHEEP'S HEART, DESIGNED TO SHOW THE DIF- 

 FERENT DEGREES OF OBLIQUITY OF THE FIBRES. 



(Allen Thomson. ) 



At the base and apex the superficial fibres are dis- 

 played : in the intervening space, more and more of 

 the fibres have been removed from above downwards, 

 reaching to a greater depth on the left than on the right 

 side, a 1 , a 1 , the superficial fibres of the right ventricle; 

 & 1 , 6 1 , the same of the left ventricle ; at 2 these fibres 

 have been removed so as to expose those underneath, 

 which are seen to have the same direction as the super- 

 ficial ones over the left ventricle, but different over the 

 right ; at 3 some of these have been removed, but the 

 direction is only slightly different ; 4, transverse or 

 annular fibres occupying the middle of the thickness 

 of the ventricular walls ; 6, 7, internal fibres passing 

 downwards towards the apex to emerge at the whorl ; 

 between c, c, the anterior coronary or interventricular 

 groove, over which the superficial fibres are seen cross- 

 ing ; in the remaining part of the groove, some of the 

 deeper fibres turn backwards into the septum ; d, the 

 pulmonary artery ; e, the aorta. 



constantly branched and united to one another so as to form a complete network or 

 spongework with reticulating interstices. They are moreover composed in the manner 

 described in Volume I. (p. 304) of somewhat oblong occasionally forked cells, cemented 



Fig. 324. MUSCULAR FIBRES FROM THE HEART, MAGNIFIED, 



SHOWING THEIR CROSS STRLE, DIVISIONS, AND JUNCTIONS. 



(Schweigger-Seidel.) 



The nuclei and cell-junctions are only represented on the 

 right-hand side of the figure. 



together end to end (fig. 324). The interstices 

 between the fibres are filled by connective tissue, 

 with numerous blood-vessels, lymphatics and nerves. 



Vessels. The muscular substance is supplied 

 with blood by tffe coronary arteries, the origin 

 and course of which, as well as of the cardiac veins, 

 are elsewhere described. The smaller branches 

 penetrate into every part of the muscular sub- 

 stance, the capillaries being very numerous and 

 closely arranged. The cardiac valves are non- 

 vascular, except where muscular tissue occurs in 

 them, as is sometimes the case in the auriculo- ventricular valves (L. Langer). 



Lymphatics. The lymphatics (which are found in great number beneath both 

 the epicardium and endocardium) are also, as was shown by Schweigger-Seidel, 

 extensively distributed throughout the muscular substance, occurring in the form of 

 freely communicating fissure-like spaces between the muscular bundles, and lined by 

 endothelial cells, the mode of origin being thus to a certain extent lacunar. 

 According to Skwartzoff, whose observations were made upon the heart of the rabbit, 

 dog, and calf, the lymphatics of the ventricles are independent of those of the 



