38 THE NECTURUS 



Constrictor arcuum 



On the ventral side of the skull, deflect the ceratohyoids 

 outward and press out the branchial arch in order to see 

 the constrictors. 



There are three of these small constrictors. The more 

 anterior is between epibranchials 1 and 2, the second be- 

 tween epibranchials 1 and 3 and the third and smallest is 

 between epibranchials 2 and 3. 



Depressor arcuum branchiarum 



Ventral and lateral to the constrictors this muscle is 

 inserted on epibranchial 3. It depresses the gills. Note 

 its origin on the floor of the visceral skeleton. It is seen 

 better from the dorsal side of the visceral arch. After the 

 depressor has been removed, the dorsal side of the sterno- 

 hyoid is seen beneath it. 



