36 THE FROG 



dorsal aorta passes posteriorly, giving off branches to the 

 viscera and body wall, and bifurcates near the posterior end 

 of the body cavity. 



(o) Branches of the systemic artery. 



The small laryngeal artery arises from the dorsal surface 

 of the systemic arch near its origin. It is distributed to the 

 larynx and pharynx. 



The occipito-vertebral artery arises from the systemic 

 arch at about the level of the third vertebra; it passes an- 

 teriorly and turns dorsalward at the level of the posterior 

 end of the cranium, sending one branch anteriorly to the 

 cranium and another posteriorly along the vertebral column. 

 To trace the course of these branches turn the frog dorsal 

 surface up, slit up the skin a little to one side of the dorsal 

 median line from the tip of the nose to the "hump" of the 

 frog's back, and reflect the more lateral flap. Dissect away 

 the suprascapula (expanded dorsal portion of the shoulder 

 skeleton) and the muscles covering the dorsal surface of 

 the vertebrae. The occipito-vertebral artery will be seen 

 emerging from the body cavity just posterior to the skull ; it 

 divides into an anterior branch, the occipital artery, and a 

 posterior branch, the vertebral artery. Trace the course of 

 each. 



The small cesophageal artery arises near the angle be- 

 tween the systemic arch and the occipito-vertebral or some- 

 times from the latter. It passes to the dorsal surface of the 

 oesophagus. 



The subclavian artery arises just posterior to the occipito- 

 vertebral and passes laterally to supply the muscles of the 

 shoulder and arm. On its course toward the arm it sends 

 off several small branches to neighboring muscles and the 

 body wall. 



