GILLS OF BATRACUIA. 515 



' pcrennibrancliiate ' Batrachians, arteries are developed from tlie 

 last pair of branchial vascular arclies, as at p, fig. 344, to convey 

 blood to the hmgs. 



In Menoporna and Amplduma tlie gill-opening persists on each 

 side ; hut of the original four pairs of vascular arches only the 

 second and third accompany remains of l)ranchial arches, circum- 

 scribe the gullet, and reunite behind to form the beginning of 

 the aortic trunk. The extent of the ossification of the hyo- 

 branchial framework in some measure corresponds with the degree 

 in which the branchial organs of respiration are retained. In 

 Proteus the ceratohyals, urohyal, two pairs of basibranchials, and 

 three pairs of ceratobranchials become bony. In the Siren the 

 ceratohyals, urohyal, one pair of basibranchials, and two pairs of 

 ceratobranchials are bony. The Menopomc and Cryptobranchus 

 agree with the Newts and Salamanders (fig. 3.33), in having the 

 basihyal, ui, the ceratohyals, x, x, and two pairs of cerato- 

 branchials, y and z ; but the latter pair is projiortionally longer 

 and shows two elements of the arch, on each side, ossified. In 

 the Anourous Batrachians the branchial arches are reduced to the 

 basal portions of a single pair of ceratobranchials (ji. 91, fig. 74), 

 which persist, in most higher Vertebrates, as the ' posterior 

 cornua ' of the ' hyoid bone.' 



The \)nxis of the branchial framework in immediate relation 

 with the support of the deciduous gills never pass beyond the 

 cartilaginous stage ; and a histological test is thus aftbrded of the 

 temjDorary or permanent character of the branchiffi in a Batrachian 

 presenting them. The deciduous gills offer many modifications 

 in the larva3 of the caducibranchiate species. In a tropical South 

 American Frog (^OpisthodelpJujs ovifcra), e. g., the external gills 

 are formed before the larva is excluded, and expand into a broad 

 membranous disc at their extremity. 



But whatever the form or structure of the external gills, they 

 are fitted only to their office as such : that being discharged, they 

 turn to no other use, but lose their ciliated and vascular structure, 

 and disappear. The Tadpole, meanwhile, being subject to a 

 series of changes in evciy system of organs concerned in the daily 

 needs of the coming aerial and terrestrial existence, still passes 

 more or less time in water, and supplements the early attcmjits 

 at pulmonary respiration by pidlulating loojis and looplets of capil- 

 laries, fig. 345, a, from the branchial vessel, b, e, supported by the 

 cartilaginous arch, c, and coated by delicate non-ciliated epithe- 

 lium : the terminal processes of these ' internal gills ' support a 

 single capillary loop, d. They resemble the commencing gills of 



