36 THE NECTURUS 



Temporal 



Loosen the temporalis of the left side and follow it to 

 its insertion on the jaw, just posterior to that of the mas- 

 set er. Find all of the bones on which it originates. 



Mylohyoid 



Turn the animal to the ventral side and examine the 

 large muscle that covers the ventral region. Draw and 

 show the different direction of the fibers. What is the use 

 of this muscle? Remove the mylohyoid by splitting along 

 the midline and deflecting. 



Digastric or Depressor mandibul,e 



Look on the side of the head for this depressor of the 

 jaw. It is posterior and ventral to the large masseter. 

 There are two muscles in this region, the digastric and the 

 ceratohyoid, the digastric being the more dorsal. With 

 a blunt dissecting instrument, separate the digastric from 

 the ceratohyoid which is just ventral to it. Work out the 

 origin, insertion and function. 



Ceratohyoid 



Ventral and posterior to the digastric is a large muscle, 

 the ceratohyoid externus. Find the origin, insertion, and 

 determine the function. 



With the mylohyoid removed, the muscles of the throat 

 are easily seen, consisting of a median band of muscles, 

 the geniohyoids, the ceratohyoids extending from the pos- 

 terior angles of the skull, and the more posterior sterno- 

 hyoids. 



Geniohyoids 



This is a pair of median muscles, so closely ap- 

 pressed to one another that they work as one muscle. 



