N. ROSÉN, STUDIES ON THE PLECTOGNATHS. 



23 



ments». »To some extent», Brigde writes, »the series of 

 distal segments articulate with the longitndinal groove on 

 the distal margin of the series of proximal segments, and a 

 short, relatively stout ligament passes from each distal seg- 

 ment to subjacent proximal segments, but the articulation 

 between the two series of segments is, nevertheless, unusu- 

 ally mobile — in fact, the connexion of the distal segments 

 with one another is much more intimate than is their rela- 

 tion to the series of rigidly interconnected proximal segments.» 

 A few remarks must be made on Bridge's description, which 



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Fig. E. — Balistes vetulaL,. Diagrams of the articulation of the anal fin-rays, 

 Two different sections (see text). 



is not quite correct. The cartilaginous margin of the proxi- 

 mal segments shows alternating convex and flat areas. The 

 latter are provided with lateral pieces of fibrous cartilage, 

 thus forming articular surfaces (Fig. E II), with which the 

 distal segments of the radial elements articulate. The arti- 

 cular surfaces are cranially and caudally completed by fibrous- 

 cartilaginous meniscs, which are developed between the con- 

 vex areas of the proximal segments and the cranial and cau- 

 dal portions of the distal segments (Fig. E, I). Each menisc 

 shows three concave surfaces. Fig. E shows two transverse 

 sections through the joint between the proximal and distal 

 elements. The fin is movable mainly from side to side, very 

 little in the cranio-caudal direction as I have already pointed 



