272 Part Til. — Twentieth Annual B,ej)orl 



to some extent hidden by longitudinal striation in the last four rays. 

 The 4th to 7th rays of the cod are white, and in them the transverse 

 growth layers can be made out only at their distal tips. All the 

 branchiostegals of the lythe and saithe are more or less hyaline. 



The first branchiostegal of the lythe is to be distinguished from that 

 bone of the saithe and cod by its distinct S-shape. 



The fourth ray has certain distinctive characters. In the cod it has a 

 sort of hammer- shaped head ; in the lythe its head is rather pointed, 

 while in the saithe it is rounded, with a prominent notch on the posterior 

 edge of the head. In the saithe it is nearly round in its middle third, 

 whereas this bone in the lythe is distinctly oval in section at that part. 

 Both end in flattened extremities. 



The fifth ray of the cod is somewhat triangular in section ; in its last 

 fourth it flattens out. In the saithe it is oval in section in the middle 

 third ; in the lythe the head of this ray is smaller, but otherwise there is 

 a general resemblance between the two. They both have flat sword- 

 shaped ends. The head in the saithe is as broad as any part of the bone, 

 whereas in the lythe the head is distinctly narrower than the part of the 

 bone next it. 



The sixth ray in the saithe and lythe is a broad flat bone. In the cod 

 it is a thick bone, oval in section, flattening at the point. 



The seventh branchiostegal has a distinctly falcate proximal end. In 

 the saithe and lythe both are flat bones; the greatest breadth being at the 

 middle of their length. It is a flatter and thinner bone in the saithe 

 than in the lythe, in which the posterior edge is much thicker than the 

 anterior, whereas in the former they are both very thin. In the cod this 

 ray is widest in its last fourth. Its proximal half is thick, and its distal 

 third flat and comparatively thin. 



The Branchial Arches. 



The bones of the branchial arches are of well-marked forms, and are, 

 with one or two exceptions, easily distinguished from one another. 

 Between the lower ends of the branchial arches of opposite sides of the 

 head are the median unpaired hasihrancMals. There are four gill- 

 bearing arches. Each of the first three arches consists of three bones, 

 below the hypohranchial, above the epibranchial, and between these the 

 long ceratohrancliial. The fourth arch has an epibranchial but no hypo- 

 branchial, but is indirectly attached to the hypobranchial of the third 

 arch. The epibranchials are attached superiorly to the three uppey 

 pharyngeals. Behind the fourth branchial arch there is the lower 

 pharyngeal. It is attached by cartilage to the lower end of the fourth 

 branchial arch. The first basibranchial is attached in front to the union 

 between the basihyals of the two sides. All the articulations between 

 the bones of the branchial arches are made by means of ligaments which 

 are contained in the hollow quill-like extremities of the bones. 



The Branchial Bones of the Lythe. 



The Basihranchials (b. Br.). 



Lythe, Fig. 7, PI. IV. 



The basihranchials are three bones united together by a thick mass of 

 cartilage. The first is a hollow helmet-shaped bone. Its closed apex 

 points anteriorly, and within its posterior hollow end is lodged the front 

 portion of the thick cartilage which unites it to the broad hollow anterior 



