200 



HANDBOOK OF PHYSIOLOGY 



CIRCULATION I 



TO PA.RING 



,T0 AORTIC RING 

 L A-V, RING 



ANTR 

 INTERVENTS 



SUPERF riBRCS ENTERING MOUTH 

 OF CYLINDER TO BECOME DEEP. 



APEX- 



^-^RICINS FROM 

 PA. RING ^* 



INSERTIONS 

 IN L,A-V. 

 RING 



SUPERF LAYER 

 BECOMING 

 DEEP LAYER 



FIG. I . Section of the inaniinalian heart. .-1 .• shows the superficial fibers of the sinospiral bundle 

 sweeping toward the ape.x and entering the cylindrical layer of the left ventricle. B: shows the super- 

 ficial fibers becoming deep while turning at the apex and proceeding at right angles beneath the 

 middle layer to form the septum and the wall of an anterior papillary muscle. C: presents the full 

 course of the superficial fibers of the sinospiral bundle as they become deep and enter the left v'cn- 

 tricular cylinder. [From Grant (86).] 



NTER- 

 VENTRIC. 

 SEPTUM 



ENTERING 

 CYLINDER 

 TO BECOME 

 DEEP FIBRES 



bLindle; and ^) the deep Ijulbospiral bundle. The.se 

 bundles originate in the fibrotendinous ring structure 

 at the base of the heart and converge in a spiral fission 

 toward the apex where they form a vortex before 

 running upward and returning via a spiral pathway 

 to the opposite side of the fibrotendinous ring from 

 which they began. As shown in figure i the super- 

 ficial bundle and the sinospiral and the deep sino- 

 spiral bundle envelop portions of both ventricles, 

 whereas the deep bulbospinal muscle encircles only 

 the left ventricle. The superficial bulbospiral and 

 sinospiral bundles originate laterally on their respec- 

 tive ventricles and sweep toward the apex, enveloping 

 part of the opposite ventricle whereupon they burrow 

 beneath the middle layer, which is comprised of the 

 deep bundles, and return most deeply and at right 

 angles to their original course to form the interior 

 of the ventricles and the papillary muscles. The deep 

 sinospiral bundle composes primarily the middle 

 layer of the right ventricle, although its fibers ramify 

 around both ventricles. The deep bulbospinal en- 

 circles the left ventricle at its base, does not reach the 

 apex, and hence is unique among the bundles in being 

 the possession of only one chamber. These relations 

 are shown in figure i . 



Contraction of the deep and superficial layers 

 serves to shorten the ventricles along their major 

 axis, and contraction of the middle layer reduces 

 their transverse diameters. According to Rushmer 

 (206), reduction of the left ventricular cavity during 

 systole involves only a slight decrease in length, but 

 chiefly a reduction in transverse diameter. In con- 

 traction, the base of the heart descends toward the 

 apex. Although this is not consistent with the usual 

 action of a mu.scle acting from its point of origin 



(the base), it appears that one action of the sinospiral 

 fibers is to confer rigidity on the apical portion of the 

 septum which makes it a functional origin toward 

 which all parts of the heart move during systole. 



I 'asculature of Heart Muscle 



The heart muscle is nourished by the coronary 

 arteries which terminate in a rich capillary vascu- 

 lature. These capillaries form a plexus which invests 

 the individual muscle fibers. The number of capillaries 

 is three to four times as plentiful in cardiac muscle 

 as in skeletal muscle and provides an average blood 

 flow ten to twenty times as large (89). Roberts et al. 

 (203) found an average of 3,342 capillaries per cubic 

 milliliter of normal human heart muscle which had 

 an average muscle filler diameter of 13.9 y. and gave 

 a minimum of one capillary for each muscle fiber. 

 Direct coronary sinus catheterization of normal 

 human subjects and dogs has shown that the coronary 

 flow is about 100 ml per min per 100 g heart muscle, 

 and that coronary arterial blood undergoes a much 

 greater desaturation of its oxygen content than does 

 arterial blood perfusing skeletal musculature (23, 

 221). Average values for oxygen content of coronary 

 venous blood of 5 to 7 volumes per cent were found 

 as compared to 1 4 to 15 volumes per cent for mixed 

 venous blood. 



Ultrastrudiire of Heart Muscle 



The microscopic appearance of cardiac muscle is 

 somewhat different from skeletal muscle despite the 

 typical striated nature of both. Instead of longitudinal 

 fasciculi of discrete muscle cells the heart is a syn- 



