532 PEO¥. T, W. BRIDGE ON THE MESIAL 



certain Teleosts have been described by Eyder {I. c), and recently 

 in an admirable paper by Harrison (I. c). The observations to 

 be recorded here refer only to adult specimens, and hence may 

 perhaps be regarded in the light of a sequel to the embryological 

 work of these writers. 



I have purposely omitted all reference to the supportiug 

 skeletal elements of the caudal fins, for the reason that these 

 structures have already received considerable attention at the 

 hands of Eolliker, Huxley, Emery, Lotz, Eyder, and others, to 

 whose researches I have nothing to add. 



With regard to the nomenclature to be applied to the so-called 

 " interspinous " bones, aud to the segments of which they are 

 composed in different fishes, I must admit that I have experienced 

 some difficulty in the selection of suitable terms. By different 

 writers these structures have been described as " interspinous 

 bones or cartilages," " interspinalia," "fin-bearers," " pterygo- 

 phores." Eyder (I. c.) refers to the distal nodules of cartilage 

 supporting the fin-rays as " actinophores," which, from their 

 relation in the anal or dorsal fins to the hgemal or neural spines 

 of contiguous vertebrae, become interhsemal (hypaxial), or inter- 

 neural (epaxial) actinophores, the proximal divisions being spoken 

 of as " interspinous elements." Dean [4] designates the two 

 divisions of a bisegmental " interspinous bone " as " radials " and 

 " basals " — the former term applying to the ordinary dagger-shaped 

 interspinous elements, and the latter to the distal cartilaginous 

 nodules or "actinophores" of Eyder*; while Parker (I. c.) has 

 suggested the term " pterygophore " as applicable to " any radial 

 or fin-supporting cartilage in either the median or paired fins." 

 It is clearly desirable, in selecting appropriate terms for these 

 structures, that they should be equally applicable to the support- 

 ing elements not only of the unpaired dorsal, anal, and caudal 

 fins, but also to the homodynamous structures in the paired 

 pectoral and pelvic fins ; and from this point of view such terms 

 as " interspinous bones," or " interspinalia," are obviously unsuit- 

 able. " Pterygophore " is a somewhat cumbersome term, especi- 

 ally when it is necessary, as is often the case, to indicate the 

 segments of which a " pterygophore " is composed. " Eadials " 

 and " basals " are convenient terms when a fin-support is biseg- 

 mental, but scarcely so in the case of trisegmental structures. 



a 

 * The terms "baseost" and "eSxonost" have also been suggested (Cope, 



Am. Nat. 1890, p. 413). ' 



