SELF-STEERING ACTION OF THE HEART. 



73 





in their development. They are absent in man and the lower vertebrates, but in 

 birds and some mammals they are well marked (Schweigger-Seidel, Ranvier). 

 Blood -Vessels occur 



in the auriculo-ventricular 

 valves only where mus- 

 cular fibres are present, 

 while the semi - lunar 

 valves are usually devoid 

 of vessels except at their 

 base. The best figures 

 of the blood-vessels of 

 the valves are given by 

 Langer. The network of 

 lymphatics in the en- 

 docardium reaches to- 

 wards the middle of 

 the valves (Eberth and 

 Belajeff). 



Weight Of the Heart. Purkinje's fibres isolated with dilute alcohol c, cell ; 

 According to W. Miiller /, striated substance ; n, nucleus x 300. 



the proportion between 



the weight of the body and the heart in the child, and until the body reaches 

 40 kilos., is 5 grams, of heart-substance to 1 kilo, of body-weight; when the 

 body-weight is from 50 to 90 kilos., the ratio is 1 kilo, to 4 grams, of heart- 

 substance ; at 100 kilos. 3 '5 grams. As age advances, the auricles become 

 stronger. The right ventricle is half the weight of the left. The weight of the 

 heart of an adult man is about 9 oz. (1 oz. =29'2 grms.); female Si oz. (Clen- 

 dinning as a mean of 400 observations). [According to Laennec the heart is about 

 the size of the closed fist of the individual]. Blosfield and Dieberg give 34G grms. 

 for the male, and 310 to 340 grms. for the female heart. The specific gravity of 

 the heart-muscle is 1'069 (Kapff). 



47. Self-Steering Action of the Heart. 



Coronary Vessels. Many observations have been made to ascertain 

 whether the orifices of the coronary arteries are covered by the semi- 

 lunar valves during contraction of the left ventricle (Thebesius, 1739; 

 Briicke, 1854), or whether they are permanently open (Morgagni, 1723; 

 Hyrtl, 1855) Fig. 23. 



Anatomical Investigations The two coronary arteries whose 



branches do not anastomose (Hyrtl, Henle ; but this is denied by 

 Krause and L. Langer), arise from the beginning of the aorta in the 

 region of the sinus of Valsalva. The position of origin varies (1.) 

 either the origins lie within the sinus, or (2.) their openings are only 

 partially reached by the margins of the semi-lunar valves (which is 

 usually the case in the left coronary artery of man and the ox), or (3.) 

 their orifices lie clear above the margins of the valves. Post-mortem 

 observations seem to show that during contraction of the ventricle, it 

 is very improbable that the semi-lunar valves constantly cover the 

 origin of the coronary arteries. 



