THE OSTEOLOGY OF AMIURUS CATUS. 293 



tremity of which, the ceratobranchial of the 5th arch articulates, and 

 which probably represents the conjoined copulse of the 3rd and 4-th 

 and 4th and 5th arches. Similarly osseous hypobranchials are not 

 present in all the arches. The 1st and 2nd possess them (Hbi\ and 

 Hbo\) in the form of their round bones, but in the 3rd and 4th 

 {Hbr, and Z76r 4 ) they i-emain cartilaginous, and in the 5th appear to 

 be wanting. Oeratobranchials (Cbr U5 * are present in all the arches ; 

 they are long slightly curved bones, grooved on the under surface 

 for the reception of the branchial vessels and nerves, and carry the 

 majority of the gill-leaflets. The ceratohyal of the 5th arch (Cbr 5 ) 

 however, departs from the normal type. It is flattened from side to 

 side, is not grooved below, has no branchial leaflets, but bears on its 

 upper edge an oval plate of bone possessing a large number of teeth ; 

 this is usually known as the hypopharyngeal {Phi). The epibran- 

 chials (Fig. 4, Ebr^) also bear gill-leaflets to a certain extent, at least 

 those of the 1st and 2nd arches do. These resemble slightly the 

 ceratobranchials, but do not possess so deep a groove on the under 

 surface, being flattened. From near the middle of the posterior 

 border of the 3rd epibranchial a strong process (pro) passes back- 

 wards, inwards and upwards, serving for the attachment of muscles. 

 The 4th epibranchial {JEh\) is very broad towards its inner extremi- 

 ties, while the 5th is wanting. The pharyngobranchials are rudimen- 

 tary also. The 1st is wanting or represented only by cartilage ; the 

 2nd (Pbr 2 ) acts as a copula between 2nd and 3rd epibranchials ; the 

 3rd (Pbr s ) has a similar relation to the 3rd and 4th epibranchials ; 

 while the 4th and 5th are wanting. Thus none of the elements of 

 the upper moiety of the 5th arch are present. Lying on the under 

 surface, and attached to the 3rd pharyngo branchial and the inner ex- 

 tremities of the 3rd and 4th epibranchials, is a round osseous disc 

 bearing numerous teeth — the epipharyngeal (PhS). To the anterior 

 edges of the cerato- and epibranchial, and to both the anterior and 

 posterior edges of some, are attached a number of small rays equiva- 

 lent to the branchiostegal rays of the hyoid arch. These are readily 

 removed from the arches along with the soft parts. 



The only points to be noticed here in connection with the branchial 

 arches are the relations of the epi- and hypopharyngeals. These 

 bones are not inherent parts of the branchial arches, as is frequently 

 supposed, but have become secondarily united to them. This is indi- 

 cated by the fact that they do not belong to the same arches ; the 



