FIBRES OF THE HEART. 511 



The cavity of this ventricle Is supposed to be smaller than 

 that of the right: but the amount of the diffcM-ence has not been 

 accurately ascertained. 



This ventricle must have much more force than the right, as 

 its parietes are so much thicker. Their thickness often exceeds 

 half an inch. 



The difference in the strength of the two ventricles probably 

 corresponds with the diflerence between the extent of the pul- 

 monary artery and the aorta. 



The thickness of the septum between the ventricles is thicker 

 than the sides of the parietes of the right ventricle, and less 

 thick than those of the left. 



The muscular fibres of the heart are generally less florid 

 than those of the voluntary muscles ; they are also more 

 closely compacted together. The direction of many of them is 

 oblique or spiral ; but this general arrangement is very intricate : 

 it is such, however, that the cavities of the heart are lessened, 

 and probably completely obliterated, by the contraction of 

 these fibres.* 



— The muscular fibres of the heart have been carefully stu- 

 died by Wolf and Malpighi, and more recently still, by Mr. 

 Searlef and M. Gerdy.J According to this latter anatomist, 

 there is a fibrous zone or girdle formed around each auricle 

 and arterial orifice of the heart, which zones are connected 

 with each other and with the valves. From these zones origi- 

 nate all the muscular fibres of the heart. Some which run 

 upwards and turn in every direction round the auricles, and 

 form loops, the extremities of which are inserted on the oppo- 

 site sides of the zone. Others which run downwards and em- 

 brace the ventricles, are also inserted on the opposite sides 

 of the same zone, or that which surrounds the orifices of the 

 aorta or pulmonary artery. The structure of the ventricular 



* Mr. Home has given a precise description of the muscular fibres of the 

 heart in his Croonian Lecture. London Philosophical Transactions for 1795, 

 part I. page 215. 



f Cyclopedia of Anatomy and Physiology. London. — Article — Fibres of 

 the heart, of which he has given a minute and lengthened description. 



I Journal Complementaire du Diet, des Scienc. Med. torn. ix. p. 97. — 



