THE PERCH 221 



The cranium, as we have already seen, is composed of the 

 cranium proper and the special-sense capsules. The former, 

 which is the brain case, contains the following bones: the oc- 

 cipitals, parietals, frontals, sphenoids, ethmoids, and parabasal. 

 The sense capsules inclose the auditory, optic, and olfactory 

 organs. The auditory capsule is made up of the otic bones. The 

 optic capsule does not ossify, but remains largely membranous ; 

 the sclera of the eyeball, however, contains cartilage, and the 

 suborbitals appear around the orbit. The nasal capsule contains 

 the nasals and the vomer ; the ethmoids also enter into relations 

 with the hinder part of it. 



Exercise 27. Draw the ventral aspect of the cranium on a scale of 2, 

 showing outlines of the bones. 



Exercise 28. Draw the lateral aspect. 



Boil the cranium until the bones can be separated from one 

 another, and study them carefully. 



The Appendicular Skeleton. Four median fins are present : 

 an anterior and a posterior dorsal fin, a ventral fin, and a caudal 

 fin. The framework of the two dorsal fins and that of the ventral 

 fin are essentially alike; each consists of a series of elongated 

 bones, the basals and radials. The former are long, flattened 

 plates which lie embedded between the muscles of the right and 

 left sides of the body, alternating with the haemal and neural 

 spines. Articulating with the outer end of each of these bones is 

 a radial, or fin ray, a straight, bony rod. Note the two kinds of fin 

 rays, the sharp, stiff ones, and the jointed, flexible ones. The ante- 

 rior basal does not bear a radial. The caudal fin is without basals, 

 the radials joining directly with the urostyle and the neural and 

 haemal spines. 



Exercise 29. Draw the skeleton of a dorsal fin and that of the cau- 

 dal fin. 



The Paired Fins. The pectoral fin consists of about fifteen fin 

 rays and four small basals, the latter articulating with the pec- 

 toral girdle. This structure is formed of several bones, of which 

 two articulate with the basals, the former of these bones being 



