OF THE VALVES OF THE VASCULAR SYSTEM IN VERTEBEATA. 779 



class of animals. The fibres of the external and internal layers pursue a slightly 

 spiral course. The spiral direction of the fibres here indicated is so marked in 

 the ventricles of the bird and mammal, as to influence not only the position of the 

 musculi papillares and carneae columnse, but also the shape of the ventricular 

 cavities, and the closure of the mitral and tricuspid valves. In the bulbus 

 arteriosus of the fish, the valves as a rule, may be said to be fairly within the 

 range of muscular influence, and it is interesting to note that in this struc- 

 ture, the segments vary both as regards number, size, and shape. Thus, 

 in the frog-fish {Lophius ])iscatorius)^ the origin of the bulbus arteriosus is 

 guarded by a semilunar valve, consisting of two ample and very delicate 

 segments (Plate XXIX. fig. 47 a), resembling those found in the middle-sized 

 veins (Plate XXVIII. fig. 3 ; compare with a h) ; while in the sun-fish {Orthago- 

 riscus mola, Schneider), the same aperture is guarded by a semilunar valve, con- 

 sisting of three segments (Plate XXIX. fig. 43 a be) ; the segments being analo- 

 gous in every respect to those found in the largest veins (Plate XXVIII. fig. 1 ; 

 compare with a b c). As the valve in these cases is situated between the bulbus 

 arteriosus and the ventricle, and surrounded by a fibrous ring similar to that occur- 

 ring at the origin of the pulmonary artery and aorta, it is not affected by the struc- 

 tures between which it is situated to any great extent. The semilunar valves in 

 the frog-fish and sun-fish, may therefore be regarded as connecting links between 

 the venous and arterial ones in the bird and mammal ; and that more complex 

 system of analogous valves, which is found in the bulbus arteriosus of the fish 

 generally. In the bulbus arteriosus of the skate {Baia batis), the segments occupy 

 the whole of the interior of the bulb, and are arranged in three pyramidal rows 

 of five each (Plate XXIX. fig. 38 aJc). As the segments in this instance are 

 very small, and altogether inadequate to the obliteration of the bulbus cavity, they 

 must be looked upon as being useful only in supporting the column of blood in its 

 onward progress ; it being reserved for the segments at the termination of the bulb, 

 which are larger and more fully developed, to effect the closure. The action of 

 the segments in the bulbus arteriosus of the skate, is rendered more perfect by the 

 pressure from without, caused by the contraction of the bulb itself {d). In the 

 bulbus arteriosus of the sturgeon (Accipenser sturio), the segments are arranged in 

 three rows of eight each (Plate XXIX. fig. 39 «). They are more delicate, and less 

 perfectly formed than in the skate. In the bulbus arteriosus of the American 

 devil-fish {Cejyhalopterus giorna), they increase to thirty-six, are more imperfect 

 than in any of the others, and are supported by three longitudinal angular mus- 

 cular columns. As these segment-bearing columns, from their shape, project 

 into the cavity, so as almost to obliterate it during the contraction of the bulb, 

 they in this way bring the free margins of the segments together. The orifices of 

 the bulbus arteriosus, however, are not closed by the imperfect segments referred 

 to ; these being guarded by two well-formed and fully developed tri-semilunar 



