436 



THE DOGFISH 



second to the fifth in Fig. no) 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 corre- 

 sponding 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. III). The first arch (l) gives 

 rise in the adult frog to the carotid 

 trunk (<ra), 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 (/). 



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. 112). 

 The five afferent branchial arteries 

 [of. br I — 5) of either side do not arise 

 regularly and symmetrically from the 

 ventral aorta, as represented in the 

 diagrammatic Fig. no. 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 on the 

 hyoid arch and the holobranch of the 



Fig. hi. — 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 

 Anatomy^ after Boas.) 



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 close together, and supply the 

 gills on the third and fourth branchial arches respectively : it will be 

 remembered that the fifth branchial arch bears no gill-filaments. After 



