254 THE HEART, BY F. SCHWEIGGEK-SEIDEL. 



of these valves consists essentially of two lamellse, a fibrous and 

 an elastic ; the former is directly continuous with the fibrous 

 rings, the latter in the case of the venous valves is a prolonga- 

 tion of the endocardium of the auricle, but in the arterial valves 

 it is a prolongation of the membrane lining the ventricular 

 chambers. The free surface of" the fibrous layer is invested by 

 a thin membrane composed of cells which do not rest upon any 

 special elastic substratum, except that perhaps the elastic element 

 of the fibrous layer itself undergoes a slight thickening at the 

 margin. In the semi-lunar valves the elastic layer is considerably 

 thickened, whilst at the attached border of the venous valves 

 the two layers disappear towards their apices, their place being 

 supplied by the tolerably abundantly nucleated tendinous tissue 

 of the chordae tendinese. The latter near the musculi papillares 

 possess an external elastic layer with a delicate investing 

 membrane composed of cells, which constitutes a prolongation 

 of the endocardium * At the apices of the valves muscular 

 bundles pass directly into the endocardium of the auricle, and 

 extend to a greater or less distance downwards, but in all 

 instances are limited to the upper portion.*}* 



According to the statements of Oehl, J small isolated muscles are pre- 

 sent in the larger tendinous cords of the left auriculo- ventricular valves. 

 The fibres of Purkinje are continuous with the chordas tendineae. 

 Yillous processes or outgrowths are sometimes found attached to the 

 valves (Luschka, Lambl.). In regard to the endocardium in general, it 

 should be mentioned that the microscopic appearances which are found 

 in various animals differ chiefly in the greater or less development of 

 the elastic network of fibres. The foregoing description is chiefly taken 

 from observations made on the heart of man. 



* Analogous observations were formerly made by Donders, in regard 

 to the structure of the valves. I cannot agree with the statement of 

 Luschka, that the valves are the direct continuation of the arterial wall, 

 Archiv fiir Physiologische Heilkunde, 1856, p. 537 ; compare also Henle. 



f Amongst the most recent investigations on the musculature of the 

 auriculo- ventricular valves are to be enumerated those of Gussenbauer, 

 Sitzungsberichte der Wiener Akademie der Wissenschaften, Band Ivii., 

 Abth. 1. 



J Mem. d. Acad. d. Scienze d. Torino, Vol. xx., 1861. 



