478 ANATOMY OF VERTEBEATES. 



short tube above each pectoral fin. The power of existing 

 long out of water depends chiefly on these mechanical modi- 

 fications for detaining a quantity of that element in the 

 branchial sacs ; for fishes perish when taken out of water, chiefly 

 by the cohesion and desiccation of their fine vascular branchial 

 processes, through which the blood is thereby prevented from 

 passing.' If suflScient water can be retained to keep the gill- 

 plates floating, the oxygen which is consumed by the capillary 

 branchial circulation is supplied to the water retained in the 

 branchial sac directly from the air. In some of the Eel tribe the 

 small branchial outlets are closely approximated below, as in 

 Sphagehranclius ; and they are blended into a single orifice in 

 Symbranchus, analogous to that in the Myxine. In some Ganoids, 

 many Plagiostomes, fig. 13/, br, and all Sturgeons, a canal leads 

 from the fore part of each side of the branchial chamber to the 

 top of the head ; the outlets are called ' spiracles,' the canals 

 ' spiracular.' The nasal sac communicates in the Lamprey with 

 the single homologous canal, the inner or faucial aperture of 

 which is shown at c, fig. 277. 



The branchial chamber is largest in the fishes which have the 

 smallest outlets, as, e.g., in the Eel tribe, the Uranoscopi, the 

 Blennies, and especially the Lophioids : extending backward in the 

 Angler (^Lophius piscatorius) towards the hind part of the abdomen, 

 with a proportional elongation of the branchiostegal rays ; and 

 still further back in lialieutea. The opercular flaps formincr the 

 outer wall of the gill-chambers are described at pp. 123, 124, 

 fig. 84 ; the branchial arches at p. 106, fig. 85. The basi- 

 branchials are usually present only in the two or three anterior 

 arches, the others joining below directly, or by the medium of a 

 gristly plate ( Trigla) to the last basibranchial ; or terminating 

 loosely, as in Murenophis. The hypobranchials are usually 

 present only in the first or second arches : the most constant 

 elements, both as to existence and shape, are the ceratobranchials, 

 fig. 85, 47, and epibranchials, ib. 48. The pharyngo-branchials, 

 ib. 49, vary in shape and tissue ; they attach the arches to the 

 base of the skull, and develope, with the anterior epibranchials, 

 fig. 325, the complex labyrinthic appendages of the branchial 

 apparatus in the Climbing Perch (Aiiabas) and its allies. In 

 Lophius and Diodou there are only three pairs of branchial arches. 

 The fissures between the arches become shorter as they recede in 

 position, the last being commonly a mere foramen : their vertical 

 extent shows an agreement with that of the outer gill-slit: they 



' CVI. j). 124. 



