482 ANATOMY OF VEKTEBRATES. 



The concave borders of the branchial arclies are usually beset 

 Avith defensive processes, fringes, or tubercles, and these sometimes 

 support small teeth which aid in deglutition ; but the chief office 

 of these appendages, which project inward toward the mouth, is to 

 prevent the passage of any particles to the interspaces of the gills, 

 which might injure or irritate their delicate texture. In the 

 edentulous Sturgeon andPaddlefish each arch supports a close-set 

 series of such retroverted slender tapering filaments, fig. 276, 

 which are longer than the opposite branchial processes, ib. u : 

 they are developed even from the fifth or pharyngeal arch, wliich 

 has no gill. Similar fringes of extreme delicacy defend the 

 branchial slit in the Gray Mullet. Frequently such a fringe is 

 developed only from the first branchial arch, Mackarel, Perch, 

 fig. 85, 6.1, the rest supporting dentated tubercles, fig. 321, and 

 the last or pharyngeal arch being beset with teeth only. In the 

 Rcmora and many other Fishes, the defensive tubercles on 

 opposite sides of the same branchial fissure interlock, like the 

 teeth of a cog-wheel. In the Lcjiidosiren armectens, fig. 316, 

 short valvular processes are developed from the sides of those 

 branchial fissures only which lead to the gills, the first and second 

 arches having no gills. In the Conger, all the brancliial arches 

 are devoid of defensive fringes or tubercles.' 



The immediate force of the heart's contraction is applied by a 

 short and rapidly divided arterial trunk, fig. 308, B, upon the 

 branchial circvilation. Only in a few fishes is the heart removed 

 backward from the close jn'oximity of the gills, and then the 

 branchial artery is proportionally elongated ; as in the Eel tribe, 

 especially the Si/nhranchidce : the artery is long in the Planirostra, 

 fig. 276, .5. The primary branches are always opposite and sym- 

 metrical, but vary in number in different species. Very commonly, 

 as in the Perch, they are three in number on each side ; the first 

 branch dividing, as in fig. 308, B B, to supply the fourth and third 

 gills, the second going to the second, and the third to the first 

 gill, ib. h, be. In the Polyjyterus and Skate there are only two 

 primary branches on each side : the first supplies the three poste- 

 rior gills ; the second, formed by a terminal bifurcation of the 

 In-anchial trunk, su]iplics the anterior gill in the Polypterus, and 

 in the Skate bifurcates to su]>ply also the uniserial, opercular, or 

 hyoid gill. Tlic Fox-Shark (.lAyi/V/.s-) and the Lcitidosteus give 

 examples of four pairs of ])rin\ary branches from the branchial 



So 



pi-L'p. 1038. (Con;;cr), .Tiid its lU'Scription, XX. 18.34, p. 83. 



