514 



ANATOMY OF VERTEBRATES. 



loop, but speedily expanding, lengthening and branching into 

 lateral processes with corresponding looplets ; these blood-channels 



intercommunicating by a capillary network, as at d, fig. 343. The 



gill is covered by ciliated 



343 



gills are 



One of the gills of the Newt, magn. cclxvtii. 



scales, ib. e, which change 

 into nonciliated epithe- 

 lium, f, shortly before the 

 absorbed. 

 The size of the gills is as 

 the proximity of their deve- 

 loping vascular arch to the 

 propelling organ of the 

 blood. In the Proteus 

 anguinus three pairs only 

 are developed, corresponding 

 In Siren laccrtina, as in 

 are four pairs of branchial 



344 



of branchial and vascular arches 



with the number of external gills. 



caducibranchiate Batrachians, there 



arches ; the first and fourth being fixed, the second and third free : 



their contiguous borders on the 

 concave side are provided with 

 small interlocking processes. The 

 gills are in three pairs, increasing 

 in size, according to the above- 

 stated dynamic condition, from 

 the first to the third, which is 

 attached to both the third and 

 fourth arches : the upper or outer 

 sin-face is entire and covered by 

 ordinary integument; the under 

 or inner surface is produced into 

 pinnatifid fringes, supporting the 

 capillary branchial vessels and 

 covered by thin epithelium. Each 

 gill is attached by its base an- 

 terior to and above the gill-slit, 

 which it overhangs. In the Axolotl, 

 fig. 344, the fringes of the gills are 

 longer and more slender. In the 

 Mcnobranchus they resemble those 

 of the Triton. Iu the Siren, Pro- 

 teus, and Menobranchus the outer 

 gills are persistent, and, perhaps, 

 ^^SSSSSS! o'™ Ax ° ,ot '' also in Axolotes. In each of these 



