THE RESPIRATORY SYSTEM 13 



any are missing. On each visceral arch cross-section note 

 the cartilaginous gill-arch and in the septum towards the 

 outer surface from the gill-arch are the cartilaginous gill 

 rays. The cut end of the blood vessel, the afferent branch- 

 ial vessel, is located just external to the center of the gill- 

 arch. This vessel brings the non-aerated blood to the gill. 

 On either side of the gill-arch is another blood vessel, usu- 

 ally injected with a yellow colored paste. These are the 

 efferent branchial vessels. Small branches of these will 

 be found in the gill filament. All of these efferent branch- 

 ial vessels collect the aerated blood and, as will be deter- 

 mined later, they unite to form the dorsal aorta. 



Drawing 8. Draw a cross-section of the entire visceral arch. 



