78 



THE COMMON FROG. 



[chap. 



each side of the throat upwards towards the back- 

 bone, and supporting on their outer sides the gills or 

 branchia, on which account they are called the 

 branchial arches. In front of these arches and form- 

 ing as it were the first of the series, is an arch which 

 ascends and becomes connected with the skull. 



Fig. 41.— Skeleton of left series of Branchial Arches of a Perch, seen from above. 

 I, glosso-hyal ; 2, 3, and 4, basi-branchials ; 5, hypo-branchials ; 6, cerato- 

 branchials ; 7, epi-branchials ; 8, styliform pharyn^o-branchials ; 9, pharyngo- 

 branchials ; 6"", inferior pharyngeal bone ; 9' and g", superior pharyngeal bones ; 

 ' 5. 6, 7, and 8, first branchial arch ; 5', 6', 7', and 9, second branchial arch ; 5", 6", 

 7", and 9', third branchial arch ; 5", 6'", and 7'", fourth branchial arch ; 6"", fifth 

 branchial arch. 



Fi^^2. — First three branchial Arches from the left side of a Perch. On the outer 

 ■ Convex) side of each branchial arch the series of closely-set gill filaments (or 

 laaflets or lamellae) are seen to be attached. On the inner (concave) side of the 

 fii^t branchial arch are the series of elongated processes (supporting minute 

 denticles) which help to prevent particles of food, or other foreign bodies, passing 

 from the mouth to the gill chamber. 



Turning now to those Batrachians which breathe 

 throughout their lives in the manner of fishes, we find 

 a corresponding system of branchial arches. Thus in 

 the Siren we find a series of gill-supporting branchial 

 arches, placed behind another arch which is connected 

 with the skull. 



But the frog passes the first part of its life in a fisli- 



