THE FORM OF THE HEART. 7 



driving mechanism. These fibres run in circles and almost transversely 

 round the ventricles, forming, when separated from the rest of the 

 musculature, a cylinder open above and below. The external layer of 

 muscle arises from the auriculo-ventricular groove, runs obliquely down 

 the ventricle, and turns in at the apical whorl ; thence the fibres ascend 

 in the internal layer to be inserted once more into the auriculo- 

 ventricular fibrous septum. These hook-shaped fibres shorten the 

 cavity of the ventricle, while the middle circular layers compress it. 

 The papillary muscles and the columns carneae shorten, approximate, 

 and at length come into close contact, pressed together by the con- 

 traction of the circular layer. Thus the many-celled structure of the 

 lower part of the ventricular cavity contracts, driving the blood out 

 of its meshes, and finally disappears, being replaced by solidified and 

 thickened walls. 



Harvey noticed this point. He writes: "Not only are the ventricles 

 contracted in virtue of the direction and condensation of the walls, but 

 further, that those fibres or bands, styled nerves by Aristotle, which are so 

 conspicuous in the ventricles of the lower animals, and contain all the straight 

 fibres (the parietes of the heart containing only circular ones) when they 

 contract simultaneously by an admirable adjustment, all the internal surfaces 

 are drawn together as if with cords, and so is the charge of blood expelled 

 with force." 1 



In consequence of the packing together and thickening of the 

 papillary muscles and fleshy columns during the systole, the extent 

 of the contraction of the muscular walls required to empty the 

 cavity is materially lessened, and their expulsive force is thereby 

 economised. The papillary muscles and columnse carneae fill up the 

 whole interior of the ventricle, with the exception of the small conical 

 space situated just behind the septum, and in the direction of the 

 aortic opening. Blood is left in contact with the auriculo-ventricular 

 valves up to the end of systole, and thus their closure is main- 

 tained. The contraction of the ventricle proceeds in a twisting manner ; 

 the blood is as it were wrung out of the cavity, and with a current 

 that naturally takes the spiral direction of the spring and arch of the 

 aorta. 



In the region of the aortic opening, the internal surface is perfectly 

 smooth, and offers a free passage to the exit of the blood. In the right 

 ventricle the conus arteriosus is also free from the presence of musculi 

 pectinati, and a space is left therein which is never completely emptied 

 of blood, although the conus arteriosus is shortened by its longitudinal, 

 and contracted by its transverse fibres. In each systole the diastolic 

 swelling of the conus disappears, and its long axis shortens. In the 

 right ventricle muscular bands cross the cavity, act as stays or " braces," 2 

 and prevent its over-distension. The musculi papillares and chordae 

 tendmese also take the part of stays in both cavities. The community 

 of the musculature determines the synchronism of the two ventricles. 

 The researches of Chauveau and Marey 3 on the heart of the horse, and 

 of Francois-Franck 4 on a case of ectopia cordis in man have yielded 

 records of this synchronism. 



1 Harvey, op. cit., eh. ii. 2 Ibid., cli. i. 



3 Mem. Acad, dc mid., Paris, 1863, tome xxvi. p. 302. 



4 "Trav. du labor, tie Marey," 1877, tome iii. p. 316. 



