950 



SCANDINAVIAN FISHES. 



Bv means of these globules and the ducts between 

 thoiii tiie wall of the air-bladder (but not its cavity, at 

 least in full-grown Herrings") is connected with the 

 perilymphatic spaces surrounding the auditory apparatus, 

 and variations of pressure may thus be transmitted from 

 the former to the latter. Tlie connexion is, however, 

 comparativelj' simple, simjder at all events than in the 

 Cyprinoids, and, as we have mentioned above (p. 826), 

 this structure in the Clupeoids has consequently been 

 regarded from a morphological jioint of view as a pri- 

 mitive stage of development of the corresponding appa- 

 ratus in the Carp-tislies. Another characteristic of the 

 Clupeoids is the connexion of tiie air-bladder not only 

 Avith the stomach, into whose posterior, pointed extre- 

 mitv the pneumatic duct opens in the Herring, but also 



behind the vent, may help us to explain the circum- 

 stance that the air-bladder is sometimes found filled to 

 distension with water^ 



The structure of the mouth is essentially the same 

 as in the Gwyniads. The shape and position of the 

 inlermaxillaries in particular show striking similarities 

 between the Herring and the Vendace. Here, however, 

 these bones are not applied so, closely to the maxillaries, 

 which are distinguished by the accession of a further 

 supplementar)- bone, situated in front of and (partly) 

 outside the posterior one, which, as well as the maxillary 

 itself, resembles in shape and position that of the 

 Gwyniads. 



Among the remaining peculiarities of the skeleton 

 we will only touch upon the shoulder-girdle, which has 



;,( \ 



Fig. 238. Left scapular arch and pectoral fin of a Herring. Natural size. ^4. from within; /J, from without. 

 pt, pu.stteinporal bone; sr.l, snpraclavieular bone; cl, clavicle; dp. ascending process from tlie anterior margin of the clavicle; sc, scapula; 

 ci; coracoid bone; per, pnecoracoid bone; pcli — 3. the several postclavicular bones; /;;•, brachial bones (inner row); lire, outer (distal) row 



with the surrounding \vater, tlic hind part of the air- 

 bladder lieing continued bv a duct wiiicii opens 011 the 

 posterior side of tiie triangular dermal Hap forming a 

 prolongation of the hind margin of the anal aperture''. 

 The coimexions of the air-bladder with the nearest en- 

 viroiHuents of the labyrintli, and the large temporal 

 aperture, which interposes only a thin and soft wall be- 

 tween those environments and the surrounding water, 

 may well be the cause of the sensitiveness to noise so 

 highly characteristic of the Clupeoids. The communi- 

 cation with the surrounding water, through the opening 



guided Parker'' to some morphological conclusions 

 highh- \\oi'tliv of attention. The postclavicle is not only 

 divided, as in the Salmon, into a row of separate bones 

 (in the Herring three, fig. 2.S8, B, i)c\, ^, 3), but also 

 situated outside the clavicle (cI), an arrangement known 

 only in the Herrings. How closely the shoulder-girdle 

 of the Herring is connected with the dermal growths, 

 a, sign of its primitive rank from a morphological point 

 of view (cf. above, p. 635), further appears both in the 

 thin, squamoid texture of the upper postclavicular bones 

 at the hind margin, and in the still more squamoid. 



" That the globules and ducts are excrescences of the air-bladder and in an embryonic state freely communicate therewifh, seems more 

 Ihan prob.able; but we know of no direct observation on this head. 



' Cf. Weber, De mire et anditu, p. 73; Bennett, Journ. Anat., Pliysiol., vol. XIV (1879 — 80), p. 405; Day, The Zoologist, ser. 3, 

 vo\. VI (1883, Jan.), p. 24. 



' Cf. Cuv., Val., 1. c, ton.. XX, p. 70. 



■^ Shoulder-Oirdle and Sternian, Roy Soc. 1868, p. 57. 



