TUB DERMAL FIN-RAYS OF FTSHES. 481 



the connective tissue, are found the dermal rays. They are 

 in the form of slender pliable rods, about five times as 

 numerous as the endo-skeletal fin-supports, which they overlap 

 (fig. 3, hpt.). The proximal half of the ray is stouter and 

 more cylindrical than the more distal region, which becomes 

 flattened and thinned out peripherally to a mere thread. 

 This ])roximal region is also harder, owing to more complete 

 calcification, and is never jointed. Some of the dermal rays 

 appear to remain unbranched and unjointed throughout life, 

 but most of them become both branched and jointed in the 

 distal region (figs. 3, 36, 37). 



The joints occur in the most irregular manner, beginning 

 either near the middle of the ray, or near its tip; some- 

 times they are numerous and close together, and at other 

 times few and far between. The pointed inner ends of the 

 majority of the dermal rays reach proximally to an even level 

 in the sheet of connective tissue surrounding them ; the fin- 

 muscles are attached to this connective tissue and to the 

 dermal rays themselves. The region where the joints first 

 appear at the distal end of the unjointed piece may be con- 

 sidered as roughly indicating the limit where the body ends 

 and the fin begins. 



This description applies almost equally well to the paired 

 fins, where, however, the rays are shorter and more fre- 

 quently jointed (fig. 37). 



The dermal rays of Oeratodns are formed of fibrous sub- 

 stance of horny consistency, which becomes calcified and hard 

 in the older regions. Here also the included cells become 

 very numerous, and in favourable preparations can be seen to 

 be provided with a multitude of fine branches (fig. 41). The 

 older and thicker parts of the ray acquire the structure, not 

 of cartilage, as stated by Giinther, but of fibrous bone. It is 

 to be noticed that the substance of the ray becomes sub- 

 divided into an inner and more fibrous region, and an outer 

 thinner layer, which appears more refringent and is more 

 thoroughly calcified (figs. 29, 34). This outer layer alone is 

 sharply interrupted at the articulations. The proximal un- 



VOL. 47, PART 4. NEW SERIES. H H 



