43 



supported bj^ a series of bones called a (bony) branchial arch. The first of these arches 

 is different from the rest, and is called the hyoid arch. It is attached to the end of the 

 hyomandibular, and consists of, 1st, the small cylindrical bone, marked 2 in the figure, 

 and called stylo-hyal; next, two broad stout bones placed end to end, 3 and c.h. in the 

 figure, the ejn-hyal and cerato-hyal ; and finally, two cubical bones placed side by side, 

 the hypo-hyals, h.h. Between the hypo-hyals of the opposite sides is inserted a bone 

 which is flattened in the median plane of the fish's body : this is usually called the 1st 

 basi-branchial, although in the sole it is connected only with the bones of the hyoid 

 arch. Above it is a cyHndrical bone called the basi-hyal or entoglossal, b.h. 



Attached to the lower edge of the epi- and cerato-hyals are a series of long bones like 

 curved spines, 3 to the epi-hyal, and 4 to the cerato-hyal. These are the hranchiostegal 

 rays, and they support a curved membrane which extends inwards from the inside of 

 the lower edge of the operculum, and in ordinary respiration closes the lower part of 

 the opercular aperture. 



The 1st branchial arch is composed of a chain of bones of which the most dorsal 

 attached to the side of the keel of the parasphenoid bone is the pharyngo-hranchial, 8, 

 next to this is the epi- branchial, 9 : these two are directed downwards and outwards, but 

 the cerato-branchial, c.b. 1, which succeeds, passes inwards and forwards; it is followed by 

 the hypo-branchial, which is joined to the median 2nd basi-branchial, b.b. 2. The other 

 arches, four in number, exhibit a similar plan of structure, but the last is much reduced. 

 The pharyngo-branchials of the 2nd, 3rd, and 4th arches are not styliform, like that of 

 the first, but are broad and flat ; the 3rd and 4th are fused together, the 2nd is united 

 to them, and all three bear teeth on their lower suifaces and form together the upper 

 pharyngeal bone. The second hypo-branchial is articulated with the third basi- 

 branchial, and the third hypo-branchial comes into slight connection with the posterior 

 end of the same median bone. The two hypo-branchials of the fourth pair of arches 

 are fused together to form a rhomboidal cartilage in the middle line behind the third 

 basi-branchial The fifth arch is represented only by a cerato-branchial on each side, 

 which meets its fellow in the middle line ; these two bones bear teeth on their upper 

 surface, and being situated in the ventral wall of the throat they bite against the upper 

 pharyngeal teeth, forming a second masticatory apparatus ; these bones of the fifth 

 arch are usually called the lower pharyngeals. The relations of the hyoid and branchial 

 arches of the opposite sides are shown in Plate XI, Fig. 4 where they are seen spread 

 out with their internal surfaces upwards. 



The pectoral and pelvic fins on each side are attached to the posterior border of a 

 bony arch which extends from the back of the skull downwards, curving first back- 

 wards and then forwards, and meeting its fellow of the opposite side at the ventral 

 edge of the body. This bony arch forms the posterior border of the opercular cleft. It 

 consists of the following bones : a. post-temporal, 25, Fig. 3, which is forked anteriorly and 

 attached by membrane to the posterior wall of the skull, the upper branch of the fork 

 being connected with the epiotic, the lower with the opisthotic ; a supra-clavicle, 26, an 



G 2 



