58 FISHES. 



the frontals, and are separated from each other by intervening 

 cartilage. 



After removal of the gill-cover and mandibnlary suspen- 

 sorium, the hyoid arch, which encloses the branchial apparatus, 

 and farther behind, the humeral arch are laid open to view 

 (Fig. 25). These parts can be readily separated from the 

 cranium proper. 



The liyoid arch is suspended by a slender styliform bone, 

 the stylohyal (29), from the hyomandibulars; it consists of three 

 segments, the cpihyal (37), ceratoliyal (38), which is the longest 

 and strongest piece, and the hasihyal, which is formed by two 

 juxtaposed pieces (39, 40). Between the latter there is a 

 median styliform ossicle (41), extending forwards into the sub- 

 stance of the tongue, called glossohyal or os lingiiale; and below 

 the junction of the two hyoid branches there is a vertical single 

 bone (42), expanded along its lower edge, which, connected by 

 ligament with the anterior extremity of the humeral arch, 

 forms the isthmus separating the two gill-openings. This 

 bone is called the urohyal. Articulated or attached by liga- 

 ments to the epihyal and ceratohyal are a number of sword- 

 shaped bones or rays (43), the hranchiostegals, between which 

 the branchiostegal membrane is extended. 



The Iranchial arches (Figs. 25 and 27) 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 fifth (56) remains dwarfed, is beset with teeth, and called the 

 lower pharyngeal bone. The arches adhere by their lower ex- 

 tremities to a chain of ossicles (53, 54, 55), hasibranchials, and, 

 curving as they ascend, nearly meet at the base of the cranium, 

 to which they are attached by a layer of ligamentous and 

 cellular tissue. Each of the first three branchial arches consists 

 of four pieces movably connected with one another. The 

 lowest is the hypobranchial (57), the next much longer one (58) 

 the ceratohranchial, and, above this, a slender and a short 



