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three pieces, whicli represent the pharyngo-branchials of 

 the three arches to which they belong. These pieces are, 

 however (and especially the anterior two), so closely bound 

 together that they may, as we have known them to do in 

 other forms, fuse up in old fish. The second pharyngo- 

 branchial {P.Iir.^) is a stout laterally compressed bone 

 articulating with the third pharyngo-branchial posteriorly. 

 It bore five teeth in one row. 



Basi branchial III. {B.Br.^). A very thin laterally 

 compressed bone, apparently wedged out of existence by 

 the large hypo-branchials II. Its posterior extremity lies 

 under and is covered by the two hypo-branchials III. 



Branchial Arch III. — The hypo-branchial is smaller 

 than in arch II., but the ventral spine is both larger and 

 longer, and articulating strongly with the same spine of 

 the other side forms a bony arch traversed by the ventral 

 aorta. The anterior spine in hypo-branchial II. is absent. 

 The cerato-branchial is grooved ventrally as in arch II., 

 but more deeply. The epi-branchial bears two large 

 tuberosities at its distal extremity. The posterior of these 

 articulates with the pharyngo-branchial III. [P.Br.^), the 

 anterior by two strong ligaments with the epi-branchial 

 IV. The pharyngo-branchial [P.Br.^) bears a strong 

 process behind for articulation with the pharyngo- 

 branchial II., and bears eight teeth in two rows. 



Basi-branchial IV. {B.Br^). — A very small nodule 

 of cartilage wedged in between the bases of arches III. 

 and IV. It is only connected with the fourth arch on the 

 ocular side, the basal elementb of this arch on either side 

 meeting in the mid-ventral line. The morphological 

 value of this cartilage cannot be determined on adult 

 material. It is obvious that the branchial arches have 

 undergone reduction from behind forwards. Thus there 

 are only three segments in the fourth arch. Now it is 



