58 VERTEBRATE ZOOLOGY 



opercular bones and the branchiostegal rays. There are four oper- 

 cular bones : the preopercular lies along and back of the hyoman- 

 dibular and symplectic bones ; the opercular is a broad bone just 

 back of the preopercular and the hyomandibular, the hinder border 

 of which is drawn out into a long spine ; the interopercular and 

 subopercular lie along the ventral borders of the preopercular and 

 the opercular respectively. 



Articulating with the ventral half of the hyoid arch are seven 

 slender arched bones, the branchiostegal rays, which support the 

 branchiostegal membrane. Note with which bones they articulate. 



Exercise 29. Draw a semidiagrammatic view of the side of the skull 

 on a scale of 2, and carefully label all the bones just mentioned. 



Remove the opercular bones and the lower jaw. Remove the 

 suborbital bones. The lateral aspect of the gill arches, the hyoid 

 bones with the branchiostegal rays, the hyomandibular, the sym- 

 plectic, and the pterygoids will be seen. Carefully clean them with 

 a brush, but do not remove them. 



Exercise 30. Draw this aspect, showing these bones. 



Disarticulate and remove the five gill arches and the hyoid 

 arch from the body. In the midventral area and joining these 

 arches is a row of median bones called the basibranchials, or 

 copulae ; the copula of the hyoid arch is the basihyal, which sup- 

 ports the tongue and has already been described. Note the gill 

 rakers, the row of short processes which spring from the gill 

 arches ; they bound the gill slits and act as strainers. Note which 

 of the arches bear teeth. 



Exercise 31. Make a drawing of the ventral aspect of the gill and 

 hyoid arches on a scale of 2 ; carefully label their various parts. 



Exercise 32. Make a drawing of the roof of the mouth and carefully 

 label all the bones already studied. 



Remove the premaxillary, maxillary, palatine, pterygoid, quad- 

 rate, symplectic, and hyomandibular bones, and study the cranium. 



The cranium is a complicated structure, made up of a large 

 number of bones and cartilages. The bones are so tightly bound 

 together that the sutures are often indistinguishable until the 



