OF THE VALVES OF THE VASCULAR SYSTEM IN VERTEBRATA. 781 



(Plate XXIX. fig. 43/), the valve is destitute of chordae tendinese likewise; but in 

 this instance the muscular fibres are arranged in the direction of the freemargino f 

 the segments of the valve, and no doubt exercise an influence upon them. In the 

 grey shark the membranous folds forming the segments, are elongated at the 

 X>arts where they are attached to the ventricular walls, these elongated attach- 

 ments being more or less split up, so as to resemble chordce tendinew. 



In the American devil-fish the semilunar valve consists of two strong well- 

 developed membranous folds, which, like the preceding, are attached by elongated 

 processes to the interior of the ventricular wall ; these processes consisting of dis- 

 tinct tendinous slips, which are attached to rudimentary musculi papillares. 



In the sturgeon (Plate XXIX. fig. 37), three tendinous chords (b) from 

 rudimentary musculi papillares, are seen to extend into the half of each of 

 the segments ; while in the left ventricle of the dugong, six chords, proceeding 

 from tolerably wellformed muscidi papillares, are distributed to the back, and 

 six to the margins of each of the segments. It is, however, in the bird and 

 mammal, particularly the latter, that the musculi papillares are most fully de- 

 veloped, and the chordse tendinese most numerous — the number of tendinous 

 chords, inserted into each of the segments, amounting to eighteen or more (Plate 

 XXVIII. fig. 33 rr, ss'). As the auriculo-ventricular valves are attached either 

 to the interior of the ventricle, or to the musculi papillares or carnese columnse, 

 it is plain that the contraction of the ventricle must influence them to a greater 

 or less extent. That, however, the presence of muscular substance in no way 

 interferes with the efliciency of the valves, is proved by the fact, that some valves 

 are partly muscular and partly tendinous, a few being altogether muscular. Thus, 

 in the heart of the cassowary, the right auriculo-ventricular orifice is occluded by 

 a valve, which is partly muscular and partly tendinous ; the muscular part, which 

 is a continuation of two tolerably well-formed musculi papillares, extending into 

 the tendinous substance of the valve, where it gradually loses itself. In the 

 right ventricle of the crocodile (Plate XXIX. fig. 42 r), a muscular valve, resem- 

 bling that found in the right ventricle of birds, exists. 



In birds the muscular valve (Plate XXIX. figs. 45 and 46 ^ A i) is usually 

 described as consisting of two parts, from the fact of its dependent or free 

 margin [g) being divided into two portions by a spindle-shaped muscular band 

 (/i), which connects it with the right ventricular wall (J). As, however, the wall 

 consists of one continuous fold towards the base {i), and the two portions of the 

 ma,rgin are applied during the systole not to each other but to the septum 

 {efe' e"'), it is more correct to say that the valve is single ; the spindle-shaped mus- 

 cular band representing the musculus papillaris of the right wall of the ventricle 

 with its attached chordse tendinese.* In the serpent, the opening between the right 



* For the relations, structure, and function, of the muscular valve in birds, see paper already 

 referred to. Phil. Trans, vol. 154, pp. 470-1-2. 



VOL. XXIII. PART ITI. , 9 Z 



