206 SUB-CLASS (AND ORDER) TELEOSTEI. 



proceeding from the air-bladder in fishes just removed from the 

 water and opened. It appears that sounds may be produced 

 in some fishes without special air-bladder muscles by the activity 

 of muscles, with the fascia of which the air-bladder is in close 

 connection (Peristedion cataphractum, Trigla lyra, Sciaena 

 aquila, etc.). 



Vascular System. The heart is without a conus arteriosus, 

 and is usually separated from the ventral aorta by two semilunar 

 valves only, though there is sometimes a small third valve. In 

 some Clupeids it is said * that a trace of a small conus provided 

 with striped muscles may be made out, and in Butirinus (Albula) 

 there are actually two rows of valves (two large and two small 

 in the proximal, and two large in the distal row). 



The ventral aorta presents at its ventricular end a swelling, 

 the bulbus arteriosus, due to the thickness (elastic tissue and 

 smooth muscular fibres) of its walls at this point. It gives off 

 branches to the four anterior branchial arches, which usually 

 bear gills. 



The ventral aorta does not as a rule give off branches to arches which 

 are without gills, but in some cases with deficient posterior gills (Sym- 

 branchus, Amphipnous, etc.) the afferent vessel from the ventral aorta 

 is present and passes round directly into the efferent vessel, so that 

 venous blood is conveyed into the dorsal aorta. As an example, we may 

 mention Amphipnous, the first branchial of which has no gills ; the second 

 has a few filaments ; the third has a transparent fringed membrane, and 

 the fourth has no gills. The breathing organs are two sacs filled with 

 atmospheric air and placed over the upper ends of the branchial arches ; 

 they open into the branchial cavity between the dorsal end of the hyoid 

 and first branchial arches. The ventral aorta gives off a branch on each 

 side, which passes to the fourth branchial arch and joins its fellow to form 

 the dorsal aorta ; it then gives off small branches to the second and third 

 branchial arches and to the air-cavities, the blood from which is returned 

 in two trunks which join the dorsal aorta. 



The blood after passing through the gills is collected by the 

 efferent branchial arteries, of which one leaves each gill-bearing 

 arch. These fall into the two roots of the dorsal aorta, which 

 anastomose in front dorsal to the parasphenoid bone and con- 

 stitute the so-called circulus cephalicus (Fig. 120, cc). The 

 circulus cephalicus gives off anteriorly the internal (at a) and 

 external (b) carotid arteries, and receives an anastomosing 

 branch from the hyoidean artery (vh) ; posteriorly it gives off the 



* J. E. V. Boas, Morph. Jahrb., vi., 1880, p. 527. 



