52 



FISH GALLEllY. 



Fig. 39. 



Hyoid and scapular arclies of Perch. 



The hyoid arch is suspended on each side by a slender styliform 

 bone, the stylohyal (29), from the hyoniandibulars ; it consists 

 of three segments — the epihyal (37), ceralohyal (38), and basi- 

 liyal (39, 40), the latter formed by two juxtaposed pieces. A 

 median ossicle, extending forwards into the substance of the tongue, 

 is called glossohyal or os linguale (41). And below the junction of 

 the two hyoid branches there is a vertical single bone (42), ex- 

 panded along its lower edge, which, connected by ligament with 

 the anterior extremity of the humeral arch, forms the isthmus 

 separating the gill-openings. This bone is called the urohyal. 

 Articulated or attached by ligaments to the epihyals and cerato- 

 hyal are a number of sword-shaped bones or rays (43), the branchio- 

 stegals, between which the branchiostegal membrane is extended. 



The branchial arches (fig. 40) are enclosed within the hyoid 

 arch, with which they are closely connected at the base. They 

 are five in number, of which four bear gills, whilst the iifth (56) 

 remains dwarfed, is beset with teeth, and called the lower 

 pharyngeal bone. The arches adhere by their lower extremities to 

 a chain of ossicles (53, 54, 55), basibranchials. Each of the first 

 three branchial arches consists of four pieces. The lowest is the 



