VALVES OF THE HEART. 181 



The deep fibres are circular, or transverse, and surround 

 each ventricle separately. 



The muscular tissue of the heart is of a 

 deep red color, and resembles, in its gross 

 characters, the tissue of ordinary voluntary 

 muscles ; but, as already intimated, it pre- 

 sents certain peculiarities in its minute anat- 

 omy. The fibres are considerably smaller 

 and more granular than those of ordinary 

 muscles. They are, moreover, connected with 

 each other by short inosculating branches, 

 while in the voluntary muscles each fibre runs 



Anastomosing muscu- 



from its origin to its insertion enveloped in iar fibres from the hu- 



r man heart. (After K61- 



its proper sheath, or sarcolemma. In the ker -> 

 heart the fibres have no sarcolemma. 1 These peculiarities, 

 particularly the inosculation of the fibres, favor the contrac- 

 tion of the ventricular walls in every direction, and the complete 

 expulsion of the contents of the cavities with every systole. 



Each ventricle has two orifices : one by which it receives 

 the blood from the auricle, and the other by which the blood 

 passes from the right side to the lungs, and from the left side 

 to the system. All of these openings are provided with valves, 

 which are so arranged as to allow the blood to pass in but 

 one direction. 



Tricuspid Valve. This valve is situated at the right 

 auriculo-ventricular opening. It has three curtains, formed 

 of a thin but resisting membrane, which are attached around 

 the opening. The free borders are attached to the chordae 

 tendinese, some of which arise from the papillae on the inner 

 surface of the ventricle, and others directly from the walls of 



1 ROBIN states (Dictionnaire de Medecine, etc., de P. H. Nysten, onzieme edition 

 par E. Littre et Ch. Robin. Cceur.) that the fibres of the heart have no sarco- 

 lemma, which I believe to be the fact, though Kolliker (Manual of Microscopic 

 Anatomy, London, 1860, p. 477) says: " Their sarcolemma is very delicate, or even 

 may not be demonstrable at all, except by the aid of reagents." 



