228 ELEMENTARY BIOLOGY. [XIIL 



5. Tlie aortic arches and their branches. 



a. Dissect out the branches of the aortic arches : 

 three on each side, 



a. The anterior division {carotid trunk): it, after 

 giving off a branch {Ungual artery) which runs 

 up the throat, ends in a small red body, the 

 carotid gland, from which other arteries pro- 

 ceed. 



/3. The systemic aortic arch: this is the middle 

 and largest division : it runs round the throat 

 towards the vertebral column, giving off on 

 its way the subclavian artery which runs to 

 the fore-limb. 



7. The pulmo-cutaneous artery, or posterior division 

 of the aortic arch : it runs to the root of the 

 lung, giving off on its way a cutaneous branch 

 which runs out to the integument about the 

 shoulder. 



b. Imbed in paraffin an aortic arch which has been 

 hardened in spirit and cut transverse sections 

 of it : examine with 1 inch obj. Note the two 

 partitions subdividing it into three channels. 



G. Take a frog which has been in spirit for a time : open 

 its pleuroperitoneal cavity, and carefully dissect away 

 the ventral wall of the aortic bulb. Note in its cavity 

 the moveable partition or valve, fixed on its dorsal 

 border but free on the ventral. Also make out the 

 cavities of the two auricles ; the partition separating 

 them ; the spongy cavity of the ventricle ; the opening 

 between the ventricle and the bulbus arteriosus. 



