branchial arch 



■v/- 



external gill 



external gill 



external gill vestige 



internal gill 



internal gill 



Trnnur -irnnfaiuiuiini 



ABC D E 



Figure 11-15. Five early stages in the development of on aortic arch in a larval onuran. 



ductus arteriosus now connects the pulmonary artery with the 

 dorsal stem. In the tadpole the development of the aortic arch, 

 in terms of both external and internal gills, can be observed 

 (Figure 11-15). 



Choanate fishes 



Among the dipnoans there are four or five aortic arches 

 leading away from the heart: the second, third, fourth, fifth, 

 and sixth in Prolopterus (Figure 11-16). The arches bearing 

 gill filaments are fish-like with afferent and efferent divisions 

 (Figure 1 1-17). The artery to the lung arises dorsally from 

 the common efferent channel (radix aortae). The first three 

 arches have a common ventral stem as do the fifth and sixth 

 arches. Neoceratodus lacks the second efferent vessel but is 

 otherwise similar (Figure 11-17). Latimeria has not been 

 described, but, on the basis of the lungfishes, is probably 

 like the actinopterygian. 



Actinopterygian fishes 



Among the actinopterygian fishes, there are four pairs of 

 branchial arches arising from a ventral aorta. These are 

 arches 3 to 6 of the pairs observed in the embryo of higher 

 vertebrates (Figure 11-18). They are associated with five 



gill openings derived from pharyngeal pouches. Each arch 

 is broken into an afferent division taking blood to the fila- 

 ments and an efferent division collecting blood from the 

 filaments and carrying it to the dorsal aorta (Figure 1 1-19). 



In the primitive fishes, Polypterus and Amia, there is a 

 pulmonary artery leading from the sixth eflFerent vessel on 

 either side back to the swim bladder. This pulmonary artery 

 has the same association observed in the choanate fishes. In 

 most actinopterygians, the dorsal aorta supplies the swim 

 bladder (Figures 9-31, 9-32). 



In Acipenser or Lepisosteus, the second afferent arch is pre- 

 sent and serves the hyoid hemibranch (Figure 9-35). The 

 spiracular, or mandibular hemibranch, is served by the ef- 

 ferent vessel of the hyoid hemibranch and the efferent vessel 

 of the first branchial arch (3). In the more advanced fishes, 

 with the loss of the hyoid hemibranch, the second (hyoid) 

 afferent has been lost or replaced by connection with the 

 efferent vessel of the first branchial arch. The pseudobran- 

 chial circulation is variable, but generally only oxygenated 

 blood reaches this gill. The efferent pseudobranchial artery 

 supplies the eye. 



Chondrichthyes 



In the sharks there are six pairs of aortic arches or more 

 depending upon the number of branchial arches (Figure 



.efferent pseudobranchial 



gill raker, 

 internal carotid 



monary 



efferent artery 

 afferent artery 



B 



Figure 1 1-16. Aortic arches of Protopterus as seen from below. A, and a cross section of a gill 

 showing interrelationships of main ports, B. 



350 • THE CIRCULATORY SYSTEM 



