253 



THE HEART. 



of tlie Yulves, strengthened on the sides next the septum by tlie 

 processes from tlie fibro-cartilago. The rings of tlie arterial orifices 

 give attachment below to some of the muscular fasciculi of the ventricle, 

 whilst above they present an uneven edge with three deep semilunar 

 notches, to which the middle coat of the artery and the flaps of the 

 valve are iirmly attached. The fibres of the middle coat of the artery, 

 here comparatively thin, are not arranged annulai'ly, as in other parts 

 of the vessel, but converge to the intervals between the sinuses of 

 Valsalva, to be attached to the fibrous rings. 



The tendinous rings of the aortic and left amicular orifices are con- 

 fluent, so that when the fibrous tissue is destroyed by boiling the two 

 apertures run into one. 



are seen 

 them. 



Fig. 175. — Anterior view of 

 Heart op a Young Subject 



DISSECTED after BOILING, TO 



SHOW THE Superficial Mus- 

 cular Fibres, two-thirds 



THE NATURAL SIZE. (AlleU 



Thomson). 



Tliis figure is planned after one 

 of Luschka's, but its details were 

 chiefly taken from an original 

 ineparation. The aorta, V, and 

 pulmonary artery, n', have been 

 cut short close to the semilunar 

 valves, so as to show the anterior 

 fibres of the axaricles. «, super- 

 ficial layer of the fibres of the 

 right ventricle ; h, that of the 

 left ; c, c, anterior interventricu- 

 lar groove, from which the coron- 

 ary vessels have been removed, 

 (7, right auricle ; d' , its appendix, 

 lioth showing chieflyperpendicular 

 fibres ; c, ui>per part of the left 

 auricle ; between c, and V , the 

 transverse fibres which behind the 

 aorta pass across both auricles ; 

 c', appendix of left auricle ; /, su- 

 l^erior vena cava, around which, 

 near the auricle, circular fibres 

 ; y, 'J, right and left pulmonary veins with circular bands of fibres surrounding 



Muscular tissue. — The microscopical characters of the muscular 

 tissue of the heart have been already considered (p. 119). It remains, 

 however, to notice the general course and arrangement of the 

 fasciculi (or " fibres," as they are ordinarily termed), in the auricles 

 and ventricles respectively, for the muscular bundles of the two are 

 not continuous, being only connected by the fibrous tissue around the 

 auriculo-veutricular orifices : in conformity with this it is seen that 

 after boiling the heart the auricles may be easily separated from the 

 ventricles. 



Fibres of the auricles. — These consist of a superficial set, common 

 to both cavities, and of deeper fibres proper to each. The siqm-ficial, 

 common or trausim-fif fibres run transversely over both venous sinuses, 

 near the base, and ai'e most numerous on the anterior surface 3 



