VASCULAR SYSTEM OF FISHES. 257 



The ventricle {fg. 61. y) usually presents tlie form of a four-sided 

 pyramid, one side dorsad towards the auricle ; one angle ventrad, and 

 the base forwards. In the Lepidosteus and Polypterus, however, it 

 is pyriform : in the Pike it is lozenge-shaped : in the Lophius, as in 

 the Myxinoids and Lampreys, it is oval : in most Plagiostomes its 

 transverse diameter is the longest, as if preparatory to a division. 

 Its cavity is, however, simple in all fishes. The parietes of the ven- 

 tricle are very muscular, and the fibres are redder than those of any 

 other part of the muscular system ; but the colour is less deep in the 

 ground-fishes than in those that swim nearer the surface, and enjoy 

 more active locomotion and respiration. The exterior muscular fibres 

 decussate and inteHace together irregularly and inextricably ; but 

 the deeper-seated ones form more regular layers, the innermost being 

 transverse and circular, and separating readily by slight decomposi- 

 tion from the outer and more longitudinal layers. Some of the in- 

 ternal fasciculi send off' the 'chords tendineoi' above mentioned in 

 the Sturgeon ; but in almost all other fishes those 'chords' are absent, 

 and the auricular valve is free. In most osseous fishes the orifice at 

 the base of the bulbus arteriosus is provided with a pair of semilunar 

 valves (prep. 606.): the Sun-fish (prep. 905.) has four such valves 

 there. But the Ganoids, Holocephali, and Plagiostomes have two 

 or more transverse roAvs of semilunar valves attached to the inner 

 surface of their long and muscular bulbus arteriosus. The prepara- 

 tion, No. 911., shows two rows of three valves in the Grey Shark 

 {Galeiis); the same is found in the Blue Shark (C«?t/*«?705), in 

 the Dog-fish (Sci/llimn), and in the Chimasroids : the Amia has two 

 rows of six valves : in the genera Sjihyrna, 3Iustdus, Acanthias, 

 Alopias, Lamna, RJdnohotus, Torpedo,iind Accipetiser there arc three 

 rows of valves: the preparation of the Sturgeon's I'eart (No. 908.) 

 shows five valves in the anterior row, and four valves in each of the 

 other rows ; and the free margins of the valves are connected by short 

 ' chordaj tendinea3' to the parietes of the bulb. The genera Hexanthus, 

 Ileptanchns, Centrophoriis, and Trygon have four rows of valves. The 

 preparation of the heart of the Raia Batis (No. 909.) shows five rows, 

 the valves increasing in size to the last row, which is at the termina- 

 tion of the bulb. Scymnits, Sfpiafnta, and Myliohates have also five 

 rows of valves. In the Cephaloptera the large bulbus arteriosus* 

 presents internally three longitudinal angular ridges, at the sides of 

 which are small valves disposed in pairs, and in four or fixe rows: 

 besides these there are three larger valves at the beginruig, and three 

 at the end of the bulb. The valves are still more numerous in the 



* I found its eavhy more capacious tlian that of the contracted ventricle. 

 VOL. II. S 



