THE PERCH 6 1 



bones forming the anterior end of the cranium proper and the 

 hinder end of the nasal capsules. 



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 occipitals, 

 parietals, frontals, sphenoids, ethmoids, and parabasal. The sense 

 capsules inclose the auditory, optic, and olfactory organs. The au- 

 ditory 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 certain membrane 

 bones, the suborbitals, appear around the orbit. The nasal cap- 

 sule contains the nasals and the vomer ; the ethmoids also enter 

 into relations with the hinder part of it. 



Exercise 35. Draw the ventral aspect of the cranium on a scale of 2, 



showing outlines of the bones. 

 Exercise 36. 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 anterior 

 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 37. Draw the skeleton of a dorsal fin and that of the 

 caudal 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 



