THE SKELETON OF CODFISH. BRANCHIAL ARCHES. 101 



Interposed between the hypo-hyals of the two sides is an 

 unpaired somewhat triangular plate, the uro-hyal or basi- 

 branchiosteyal (fig. 12, 15). 



THE BRANCHIAL ARCHES. 



The branchial arches are five in number and consist of 

 the following parts on each side. The dorsal end is formed of 

 the supra-pharyngeal bone, a large irregular bone covered 

 ventrally with teeth of a fair size, and representing the fused 

 pharyngo-branchials of the four anterior arches. Its external 

 surface is continuous with four small epi-branchials which 

 pass horizontally backwards and outwards. Their distal ends 

 meet four long cerato-branchials which are directed for- 

 wards and inwards and form the principal part of the arches. 



Each of the first three cerato-branchials articulates ven- 

 trally with a hypo-branchial, and the hypo-branchials of 

 the two sides are united in the middle line by an unpaired 

 basi-branchial. The third hypo-branchial is much flattened. 

 The fourth cerato-branchial is united by cartilage with the 

 posterior surface of the third hypo-branchial, which it meets 

 near the middle line. 



The fifth arch consists only of the cerato-branchial, a wide 

 structure covered with teeth and generally called the inferior 

 pharyngeal bone. 



The skeleton of the operculum consists of the same four 

 bones as in the Salmon, namely the opercular, the infra- 

 opercular, the pre-opercular and the sub-opercular. Of these 

 the anterior bone, the pre-opercular, is the largest, while the 

 infra-opercular is the smallest. The opercular has a facet for 

 articulation with the hyomandibular. 



2. THE APPENDICULAR SKELETON. 



THE PECTORAL GIRDLE. 



This is of a highly specialised type. Membrane bones are 

 greatly developed, and the cartilage bones, the scapula and 

 coracoid, are much reduced in size and importance. 



