478 MUSCULAK STRUCTURE [sect. 212. 



these fibres, small fat granules are almost uniformly found, which 



are frequently disposed in series, along with the nuclei, in the axis 



of the fibre ; and which appear very much enlarged and coloured 



when the fibres undergo degeneration. A still more important 



Fig. 193. characteristic of the muscular fibres of the heart, is 



found, however, in the intimate union of their 



elements, which lie closely upon each other, with 



very little connective tissue between them ; and 



they are also (as Leeuwenhoek pointed out, and 



as I have myself confirmed), united directly witli 



each other. Except at the inner surface of the 



heart, the fibres nowhere form distinct bundles. 



The anastomoses of the muscular fibres, which 



are a general attribute of the fibres of the heart, 



are effected in man and mammalia bv short 



rau?ve\TuKUe n s e fro r ra bundles, oblique or transverse; they are for the 



most part narrows, but are extremely numerous, 



so that at many places of the ventricles and auricles (whether 



everywhere I know not), they are met with in every small piece. 



Moreover, there occur true divisions of the fibres, by means of 



which the thickness of a separate portion of a fibre may became 



more considerable than it was at its origin. 



The course of the muscular fibres in the heart is extremelv 

 complicated, and can only be described here in a general manner. 

 The muscular fibres of the ventricles and auricles are completely 

 separate from each other ; but the chief place of origin for both 

 alike is from the ostia venosa and arteriosa of the ventricles. At 

 the former place are situated dense, tendinous bands — the so-called 

 annuli — the thinner one being in the right, the thicker in the left 

 ventricle ; these are generally described as rings situated at the 

 insertion of the venous valves, but are more accurately designated 

 as proceeding from the opening of the aorta both anteriorly and 

 posteriorly ; the densest portions of these bands is at the anterior 

 circumference of the ostia venosa, and at the part which forms 

 the partition; and from this circumstance they are also frequently 

 described as being composed of two bands, curved forwards, with 

 a posterior one situated in the auriculo -ventricular septum, and 

 splitting these into two crura. The fibrous rings of the ostia 

 arteriosa are considerably thinner than those of the ostia venosa, 

 and are situated at the origin of the semilunar valves in the form 

 of arcuately curved bands. On the auricles there are found : 

 r. fibres common to both auricles, in the form of transverse flat 



