44 ALLEN 



VI. PERIPHERAL DISTRIBUTION OF THE ARTERIES. 



I. Branchial Arteries. 



As has already been stated in the paragraph on the general 

 survey of the blood vessels, the afferent branchial arteries (Pis. 

 I and II, figs. I and 12 ; A. Br. A.) are paired vessels, which 

 convey the venous blood from the ventral aorta or branchial 

 artery (Pis. I and II, figs, i and 12 ; V.Ao.) to the branchial 

 filaments.^ They arise as 3 paired trunks from the ventral 

 aorta. The most cephalic pair supply the filaments of the first 

 branchial arches ; the second pair the filaments of the second 

 branchial arches ; and the third pair soon divide, thfe anterior 

 forks supplying the third pair of branchial arches and the pos- 

 terior forks, the last or fourth pair of branchial arches." All of 

 these vessels, which very closely resemble one another, run in 

 the grooves of their respective arches and graduall}^ exhaust 

 themselves bv giving off numerous afferent filament arteries 

 throughout their entire dorsal course. 



The Afferent Branchial Filament Vessels (PI. I, fig. 2 ; 

 A.Fil.A.) of 2 adjacent filaments arise as paired vessels, and 

 running in a caudal direction along the inner or h5'pothenuse 

 margins of their respective filaments, gradually exhaust them- 

 selves in numerous afferent jilanient cross-vessels, which are 

 only about 60 /i apart. Proximally these vessels attain a con- 

 siderable length, but gradually decrease in length distalh'. 

 Each cross-vessel terminates in a dorsal and a ventral vessel, 

 from which the fflament capillary netzvorh (P\. I, fig. 2; Fil. 

 Net.) arises. This network lies in a dorso-ventral plane in- 



' A gill or holohranch is composed of a double row of fil.ituents or 2 hcmi- 

 bratichs attached to the concave or posterior side of eacli branchial ai-ch. These 

 filaments have the form of right-angled triangles, attached b\- their short sides 

 to the arches and the hvpothenuse sides of each pair face one anotlicr. Each 

 pair of filaments is not separated hy a cartilaginous rod as is the case with the 

 Elasmobranchs, but they usually overlap one another to some extent at their 

 bases. 



2 This appears to be the normal arrangement among the Teleosts ; while in 

 the skate one trunk may supply several branchial arches, and in the ratfish 

 {Hydrolagus), I have observed that the ventral aorta gives off a pair of vessels 

 for each pair of branchial arches. 



