KI.VING-l'I.slI. 



359 



vviivos, tliis is ]ir()li;il)l\ iiotliiiiL;' iiiorc tli.-iii tlic i-dcct 

 of the current ol' air that rises i'roin the surl'ace, aiul 

 is t'oriiUMl ill the troii^^li of the wa\'es {Wi^. 'J.'i) jii^t as 

 a stream edtlies when il |)asscs a |irniiiiiiil(ir\ , nr truni 

 the same cause as that tVdiu which ihc llaine of a <'ainlle 

 is altracte(l (dwai'ds a sui'lacc, it \vc lilow straiirht to- 

 wards that surlacc thmuLih a tidic. the end ol which 

 is beside, l>ut lichind liie candle. 



Ill order to facilitate its flight the Myiii^-tisli lias 

 several peculiarities of structure. Thus we tirst observe 

 the advanced development of the pectoral fins .and the 

 shape of their rays. The tirst rav, wliicli has to divide 

 the air. is sharply compressed in the plane of the fin as 

 in the two preceding f2;enera ; lait the icst of the rays are 

 compressed in the ojipositc directimi or rather str(Migth- 

 eiied in their proximal part (the part nearest the insei"- 

 tion) l)v u downward (when tlie tins are at rest, outer) 

 edge along the anterior (when the tins are at rest, 

 superior) margin, tlie section of these rays in tiie pro- 



05. Tlie lifting oi Uio Flyiiig-fisih by tin; wind, llie (iirection 

 of which is shown bv the nrmws. .Vftcr MoBilis. 



ximal (inner) part of the tins thus forming an angle 

 opening backwards (when the fins are at rest, downwards). 

 The fin-membrane is attached to the posterior (when 

 the fins are expanded, upper) margin of the rays; and 

 the base of the pectoral fins, which, when the fins are 

 at re.st, runs upwards in front and downwards behind, 

 assumes an almost horizontal direction when the fins are 

 expanded, as the anterior (upper) rays are dra\\n down- ' 

 wards at the base, the fish thus resting on that side of 

 the fins which was formerly the exterior. On tlic un- 

 der surface of the expanded fins a deep groove, opening 

 posteriorly and interiorly, is thus formed between each 

 pair of rays; and it is in these grooves that the up- 

 ward current of air we have just mentioned, plays its 

 part in lifting the fish. 



Tile muscles of tlie pectoral fins serve chiefly to 

 expand them. They also assist to retain them in the 

 expanded position; but this oliject is also jiromoted by 

 the current of air itself, and the rays are kept in po- 

 sition tiot only by the fin-membrane but also by special 



" 0'04 oxygen, 0"94 uitrogcii ntul 0'02 carbonic acid gas; see 



ligaiiieiils. wliii-h cross from one ray to anothei- in the 

 proxiniai p.arl of the fin. Tims any extraordinary 

 strength — such as would lie necessary if the flight 

 were a true one, accoiii|Kiiiicil by the fiapping of the 

 wings — is scarcely needed, and the muscles of the 

 pectoral lliis arc hardly any thicker than in the gener- 

 alit\- of Teleosls. These nmscles are also ari'anged in 

 the usual wa\-, in two layers, a superficial and a deeper, 

 on each side of the shoulder-blades and coracoid bones. 

 The common extensory muscle of the two first (upper- 

 most) rays, however, has a long surface of origin at 

 the bottom of the clavicular groove, and has its sinew 

 inserted under a transver.se band like a roller, which 

 joins the shoulder-blade to the clavicular bone. Still, 

 the lack of an\ extraordinary degree of thickness in 

 these muscles is compensated, as in the two preceding 

 genera, by their extension. Their surface of origin, 

 the shoulder-girdle proper — the clavicular bone, the 

 shoulder-blade and the coracoid bone, especially the 

 last of these three — is also extraordinarily large here 

 as in llawph'istomn. 



The strength required to produce the great speed 

 is g'i\cn 1)\' the large lateral muscles of the body; and 

 their surfaces of origin in front — the occijuii and the 

 anterior vertebra' — are of the type we have attributed 

 above to all tlie Synentognates. Their points of insertion 

 on the last caudal vertebr:p are also strengthened. Here, 

 as in the Garpike — and we have observed similar for- 

 mations in the majority of the Mackerels — we find on 

 eaeh side of the last caudal vertebra a strong, project- 

 ing, osseous knob; and in the Flving-fish the upper 

 spinous processes of the last six or seven caudal verte- 

 bra' ai-e also longitudinally extended and contiguous. 



In the Great Flying-fish and its kindred species 

 the ventral fins also help to increase the width of the 

 fish, .ind thus also increase the size of the column of 

 air thai supports it. Their first ray is compressed ami 

 sharp, but repeatedly branched. The second ray re- 

 sembles the first, but is considerably longer; and the 

 third rav is the longest of all. 



,\s a counterpoise to the weight of the great mass 

 of niiisc Ics the Flying-fish is furnished with an extra- 

 ordinarih" large air-bladder, which occupies the greater 

 portion of the abdominal cavity (fig. 96), and is con- 

 tinned behind within the closed ha-mal arches of the 

 caudal vertebra'. In the air-bladder of the Flying-fish 

 HiMBoLDT found a strikingly small quantity of oxygen", 

 Reise yEi/ii. Geg., I, p. 309. 



