474 ANATOMY OF VEUTEBTCATES. 



the internal fasciculi send off the ' chorda? tendineae ' above men- 

 tioned in the Sturgeon; but in almost all other fishes those 

 f 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 : the Sun-fish ( Orthayo- 

 77'scM.s) has four such valves there. 1 But the Ganoids, Holocephali, 

 and Plao'iostomcs have two or more transverse rows of semilunar 



o 



valves attached to the inner surface of their long and muscular 

 bulbus arteriosus. There are two rows of three valves in the 

 Grey Shark (Galeus), in the Blue Shark (Carcharias), in the 

 Dog-fish (Scyllium), and in the Chimaeroids : the Amia has two 

 rows of six valves : in the genera Sphyrna, Mustelus, Acanthias, 

 Alopias, Lamna, Rhinobatus, Torpedo, and Accipenser, there are 

 three rows of valves: the Sturgeon's heart 2 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 ( chordae 

 tendineaa ' to the parietes of the bulb. The genera Hexanthus, 

 Heptanchus., Centrophorus, and Trygon have four rows of valves. 

 The heart of the Raia Batis 3 shows five rows, the valves 

 increasing;; in size to the last row, which is at the termination of 



o 



the bulb. Scymnus, Squatina, and Myliobat's have also five 

 rows of valves. In Cephaloptera the large bulbus arteriosus 4 

 presents internally three longitudinal angular ridges, at the sides 

 of which are small valves disposed in pairs, and in four or five 

 rows : besides these there are three larger valves at the begin- 

 ning, and three at the end of the bulb. The valves are still more 

 numerous in lepidoganoid fishes, and are arranged in longitudinal 

 rather than in transverse rows : the Polypterus shows three such 

 rows of nine or ten larger semilunar valves alternating with as 

 many rows of smaller valves. The Lepidosteus has five longi- 

 tudinal rows of sub-equal valves : those at the end of the bulb 

 being always the largest and most efficient. In the Lepidosiren 

 the place of valves is supplied in its long and twisted bulbus 

 arteriosus by two longitudinal ridges, fig. 312, c ; 5 the interesting 

 stages, which we have been tracing through the highly organised 

 Ganoids and Plagiostomes, in the partition of the bulb into 

 distinct arterial trunks for the systemic and pulmonic circulation, 

 being most advanced in this amphibious fish. 



The auricle in the Lepidosiren annectens, ib. , is essentially 

 single, but has two ear-like appendages. 6 The venous sinus 



1 xx. ii. p. 37, prep. no. 905. 2 Ib. p. 38, prep. no. 908. 3 Ib. p. 38, prep. no. 909. 

 1 I found its cavity more capacious than that of the contracted ventricle. 

 5 xxxm. p. 343. p. pi. xxvi. fig. 2. c. G Ib. p. 345. 



