THE OSTEOLOGY OF AMIURUS CATUS. 293 
tremity of which the ceratobranchial of the 5th arch articulates, and 
which probably represents the conjoined copule of the 3rd and 4th 
and 4th and 5th arches. Similarly osseous hypobranchials are not 
present in all the arches. The Ist and 2nd possess them (//br, and 
Hr.) in the form of their round bones, but in the 3rd and 4th 
(Hbr, and Abr,) they remain cartilaginous, and in the 5th appear to 
be wanting. Ceratobranchials (Cbr,;) 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 (Cobr;) 
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 hypophuryngeal (PhI). The epibran- 
chials (Fig. 4, Hbr,,) also bear gill-leaflets to a certain extent, at least 
those of the Ist 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 (#br,) is very broad towards its inner extremi- 
ties, while the 5this wanting. The pharyngobranchials are rudimen- 
tary also. The lst is wanting or represented only by cartilage ; the 
2nd (Pbr,) acts as a copula between 2nd and 3rd epibranchials ; the 
3rd (Pbr,) has a similar relation to the 3rd and 4th epibranchials ; 
while the 4th and Sth 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 pharyngobranchial and the inner ex- 
tremities of the 3rd and 4th epibranchials, is a round osseous dise 
bearing numerous teeth—the epipharyngeal (PAS). To the anterior 
edges of the cerato- and epibranchial, and to both the anterior and 
posterior edges of some, are attached a uumber 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 
