452 



THE DOGFISH 



CHAP. 



In the former there are four pairs of afferent and efferent 

 branchial arteries (corresponding to the second to the fifth 

 in Fig. 119) in relation with the corresponding branchial 

 arches and their gills. The afferent and efferent vessels at 

 first communicate with one another through the respiratory 

 capillaries, but later on each afferent becomes directly 



connected with the correspond- 

 ing efferent artery ; and at 

 metamorphosis, when the gills 

 gradually disappear, all the 

 blood thus passes directly from 

 the ventral to the dorsal aorta, 

 through the four arterial arches 

 (Fig. 120). The first arch (i) 

 gives rise in the adult frog to the 

 carotid trunk (ca), and loses its 

 connection with the second at 

 the dorsal end ; the second (2) 

 forms the systemic trunk ; the 

 third (3) disappears ; and the 

 fourth (4), losing its connection 

 with the dorsal aorta, forms 

 the pulmo-cutaneous trunk (/) 

 (compare p. 80). 



Having now traced the main 

 course and arrangement of the 

 chief arteries, there are a few 

 minor points of detail to be 

 noticed in the dogfish (Fig. 121). 

 The five afferent branchial 

 arteries (af. br i-j) of either side 

 do not arise regularly and sym- 

 metrically from the ventral 

 aorta, as represented in the 

 diagrammatic Fig. 119. The 

 anterior end of the ventral aorta 

 divides into right and left 

 branches, each of which again 

 subdivides to form the first two 

 afferent branchial arteries, which supply respectively 

 the hemibranch of the hyoid arch and the holo- 

 branch of the first branchial arch. The third afferent 

 branchial artery arises from, about the middle of the ventral 

 aorta, and supplies the holobranch of the second branchial 

 arch ; a short distance behind it the fourth and fifth come off 



FIG. 120. Diagram of the arterial 



arches of an Amphibian. 

 1-4, the four arterial arches 

 which pass up the corre- 

 sponding branchial arches ; 

 ao. dorsal aorta ; c. a. carotid 

 artery ; k. embryonic arterial 

 arch of the mandibular arch ; 

 and h. of the hyoid ; /. pul- 

 monary artery ; st. ventral 

 aorta. (From Wiedersheim's 

 Comp. Anatomy, after Boas.) 



