subclavian 



coelioc artery 



hypobranchial artery 

 A NEOCERATODUS 



anterior cerebral artery 

 iddle cerebral 

 V basilar artery 



external gills 



orbital a 



—lung 



submental' 



external carotid 



PROTOPTERUS 



Figure 11-17. Aortic arches of Neocerotodus, A, and Protopterus, B, as seen in lateral view (semi- 

 diagrammatic). (In port after Goodrich, 1930) 



1 1-20 E). The efferent vessels differ somewhat from those 

 observed in the actinopterygian in that there are two per 

 arch and the stem vessels drain adjacent ^ill bars (Figure 

 11-21). This style of drainage is suggested in Anna and 

 Neocerotodus. CUamydoselachus resembles the teleost in having 

 the mandibular arch connected with the hypobranchial ef- 

 ferent of the hyoid arch. It is distinctive in having the first 

 si.\ arches represented and a seventh as well. In Squalus or 

 Mustelus the mandibular afferent reaches only to the angle 

 of the mouth; the afferent pseudobranchial comes from the 

 efferent hyoid. The pseudobranch thus receives oxygenated 

 blood. 



The development of the arches in Squalus has been studied 

 (Figure 1 1-20). Six arches appear and for a time all are pre- 

 sent. With the separation of afferent and efferent divisions, 

 the mandibular arch becomes connected, below the level of 

 the gill pouches, with the first branchial efferent. With this 

 connective now supplying blood to the mandibular arch, the 

 mandibular afferent stem atrophies. Presence of a single ef- 

 ferent in each arch in the young shark suggests that this is 

 the primitive condition; the two efferents of the adult rep- 

 resent a modified state. 



Hydrolagus agrees with the actinopterygian fish in having 

 four complete arches which serve the four gill openings 

 (Figure 1 1-22). There is a hyoid hemibranch in front and a 

 fifth hemibranch behind. The hyoid hemibranch is supplied 

 by the second afferent arch. The efferent vessel joins the ef- 

 ferent mandibular stem or the efferent hypobranchial of the 

 first branchial arch to supply the mandibular and throat 

 areas. Hydrolagus has only a single afferent and efferent ar- 

 tery in each bar, and the efferent arteries are not joined above 

 the gill pouches as in the shark (Figure 1 1-22). 



Cyclostome fishes 



The most anterior aortic arch of the lamprey is the hyoid 

 (2), the second is the first branchial (3), and there is a gill 

 pouch between these (Figure 11-23). There are eight aortic 

 arches in all. The afferent and efferent arteries branch at 



efferent pseudobranchial 



anterior cerebra 



A LEPISOSTEUS AND ACIPENSER 



basilar artery 



opt I 

 ophthalmic 

 orbital 

 small pseudobranch (gill) 



hypobranchial 



B 



AMIA 



coeliac artery 



andibuior'^ 



C GADUS OR ESOX 



Figure 1 1-18. Semidiogrommatic lateral views of aortic arches of 

 actinopterygian fishes. A, teplsosfeus or Acipemer; B, Amio, C, Godus 

 or £sox. (After Goodrich, 1930) 



THE AORTIC ARCHES 



351 



