36 



6. — Branchial Arches (Fig. 7). 

 Ocular Side. 



Basi-branchial I. (B.Br.^). — A triang-ular bone, with 

 its apex wedged in between the upper hypo-hyals (see 

 fig. 6). At its base it articulates with basi-branchial II. 

 and with the hypo-branchials of the first arch, but the 

 latter articulation is not obvious dorsally, the head of the 

 hypo-branchial fitting into a deep lateral socket formed by 

 basi-branchials I. and II. According to Cunningham this 

 bone is in the vSole completely wedged in between the 

 upper hypo-hyals and does not articulate with the first 

 branchial arch at all. 



Branchial Arch I. — The epi-branchial {E.lh-.^) bears 

 a prominent tubercle on its anterior surface. The 

 pharyngo-branchial [P.Br.^) is a slender bone which 

 articulates with the skull at the ventro-posterior margin 

 of the jugular foramen in the prootic immediately below 

 the hyomandibular cup. This somewhat curious connec- 

 tion with the skull also exists in the Sole according to 

 Cunningham, and in SehastoJohus according to Starks. 



Basi-branchial II. (B.Br.^). — An hour glass shaped 

 bone articulating in front with the basi- and hypo- 

 branchials of the first arch and behind with basi-branchial 

 III. and slightly with the hypo-branchials of its own arch. 



Branchial Arch II. — The hypo-branchial is wide but 

 compressed dorso-ventrally. Where it articulates with 

 the second basi-branchial it sends down a prominent spine. 

 Another well-marked spine is borne on its anterior edge. 

 The cerato-branchial is longitudinally grooved ventrally. 

 As in the first arch, the epi-branchial bears a tuberosity, 

 but it is much more prominent on this arch. The first 

 and last gill rakers are very small. The superior pharyn- 

 geal bone of the Plaice in medium-sized fish consists of 



