THE CHAMBERS OF THE HEART. 



701 



Anterior cusp of aortic valve 



Portion of left ventricle, showing position ( + ) 

 of auriculo-ventricular muscle bundle in membran- 

 ous part of interventricular septum. {Rttzer.) 



2. A7isiform fasciculi, which take their origin from the auriculo-ventricular 

 fibrous ring anteriorly and extend over the auricle to insert into the fibrous ring 

 posteriorly. These bundles are situated as a rule more deeply than the annular 

 fasciculi and produce the pectinate mus- 

 cles of the auricular appendage, as well Fig. 663. 

 as certain columnar elevations, covered 

 by endocardium, which occur upon the 

 inner surfaces of the walls of the ^iricles. 

 The fasciculi common to both auri- 

 cles are developed only in the neighbor- 

 hood of the auriculo-ventricular groo\'e, 

 and constitute thin superficial bands, 

 which run parallel to the groove. The 

 anterior fasciculus is broader and more 

 highly developed than the posterior one. 

 The auriculo-ventricular fibrous ring 

 forms an almost complete separation be- 

 tween the musculature of the auricles and 

 that of the ventricles, the only direct con- 

 nection between the two being formed 

 by a slender aiiriciilo-ventriciilar fasci- 

 culus. This takes its origin in the pos- 

 terior wall of the right auricle close to 

 the auricular septum (His, Jr. ) and passes 

 downward towards the upper border of 

 the muscular portion of the ventricular 

 septum (Fig. 663). Here it bends forward and runs across the septum in the line 

 of junction of its membranous and muscular portions, and is lost anteriorly in the 

 musculature of the ventricles. The existence of this auriculo-ventricular fasciculus 

 is of considerable importance in connection with transmission of the contraction wave 

 from the auricles to the ventricles, the application of a clamp to the bundle having 

 been shown to produce heart-block (Erlanger). 



It can readily be perceived that the muscle-fibres of which the walls of the 

 ventricles are composed are arranged in more or less definite layers, and that the 

 direction of the fibres in the deeper layers is different from that of the more super- 

 ficial ones. The descriptions of the various layers and of their relations to one 

 another vary greatly jn different authors; in that given here the results obtained by 



MacCallum, by the application 

 of more suitable methods than 

 were available to the earlier ob- 

 servers, will be followed! 



The fibres of the ventricles 

 can start only from the fibrous 

 rings surrounding the ventricu- 

 lar orifices or else from the sum- 

 mits of the musculi papillares, to 

 which a certain amount of fixa- 

 tion is afforded by the chordae 

 tendineae and their attachment 

 to the auriculo-ventricular valves. 

 It will be convenient to regard 

 the fibrous rings as the principal 

 points of origin, and the most 

 sjiperficial layer of the muscula- 

 ture may be said to arise from 

 them and from the tendinous 

 band which descends upon the posterior surface of the conus arteriosus towards the 

 right auriculo-ventricular ring. Those fibres which take their origin from this ten- 

 dinous band and the right ring wind in a left-handed spiral over the surface of the 



Fig, 



Left 

 auriculo- 

 ventricular 

 orifice 



Anterior 



papillary 



muscle of 



left ventricle 



- Right 



auriculo- 

 ventricular 

 orifice 



Papillary 

 muscles 

 of right 

 ventricle 



Diagram of course of superficial muscle layers originating 

 in right and left auriculo-ventricular rings and in posterior 

 half of tendon of conus arteriosus. {MacCallum.) 



