STlli(;K.O.\-FISIlKS. 



1045 



leads into a canal which runs upwards, skirlinu' I he 

 anterior niaruin of the urcat upper suspensorium (h\-<)- 

 niiUidihular, Inn) conmnin to the whole ajiparatus of 

 the palati.' and jaws, and opens (tij:'. 2StI, sji'n) on ihe 

 top of the iiead, a little behind the eve, at ihc outer 

 margin ut tiie osseous plate eov(!riiig tiie s(pianiosal 

 part (s(jii) of the skull, and foreshadowing the s([ua- 



to the sulioperculuin and inlcropen-uluni. In the Sterlet 

 these hinielhe ai'e for tiic most part free; in the com- 

 mon Sturgeon the\- c-oalesce liiroughout the greater part 

 of tlieir extei-nal margin witii the operetdum, only their 

 to]is heing free. In one of the Ganoids (Lepidosteus) 

 MiiJ.ini" has shown tiiat the u])pt'r part of this row of 

 giil-iainina' loses its functicjual importance as a respi- 



7nosal bone. Tiie uppt'r opening is called the spiracle, ratory organ, and it is tiuis fully lioniologous with the 

 and the canal, which as well as the former is entirely ; pseudobraiichia' of the Teleosts. liehind the pharyngeal 

 absent in tiie fishes we ha 



tiie tislies We have hitherto considered, but 

 which in all higiier animals, man included, has its 

 homologue in the external and internal auditor\ meatus 

 and the tviiipanum, is liere furnished in its lower 

 (inner) part, just aliove the internal apertui-e. with a 

 row of bi-anchial hnnella'. not respiratory, however, 

 for tlie\' ar<' supplied with arterial blood. Tlie entire 



eavitv the branchial ca\it\ of (he Sturgeon shows the 

 same structuif as that of the Teleosts, four gill-arches, 

 each \\ith two rows of branchial lamella' and short, 

 scattered gill-rakers; and the fifth arch (fig. 284, Iibi%, 

 + rhr,X the lower jiharyngcal of the Teleo.sts, furnished 

 with one row of gill-rakt'rs, is here, too, destituti; of 

 branchial lameihe, and has no gill-slit behind it, lieing 



Fig. 284. Forepart of tlie endnslvcleUm in a Sturgeon. Partly after ,1. Mli.i.eh ami Pakkku. 

 B, basal angle; C, notocliord; c'i/', — cir., first — fiftli ceratobrancliial cartilages; cehi/, eeratoliyoid; fOS(, — cost^, first — eighth ribs; csp, spira- 

 cular cartilage (according to Pabkek); de, dental part of mandible; etl, lateral ethmoid; hbr^ — /(Ar,, first — fifth hypobranchial cartilages; hhi/, 

 hypohyoid; km, hyomandibular cartilage, witli the upper part covered by a parostotic disk; M, articular part of the mandible (hind part of 

 the Meckelian cartilage); m.r, maxillary; mpt, metapterygoid cartilage; ^V, n<iiral arches; Na, nasal cavity; obsp, orbitosphenoid; op*, foramen 

 of the optic nerve; /•/, palatine; pop. preoperculum (according to Pabkkr); Ps. neural spines; psp, parasjihenoid ; pt. pterygoid; 7;/, quadrate 

 cartilage; /!. n.stral cartilage: .-7./. syniplecticum; sthi/, stylohyoid; (;', foramen of the nerviit! Iriijemiiiiis; vij, foramen of tlic 



canal is analogous to a gill-slit between tln' palato- 

 niandibular and hyoid ;irches, the latter of wiiich fur- 

 nishes with its upper parts (the h\oni;iiidibulai-, fig. 

 284, Itni, and symplecticum, spl) a suspensory apparatus 

 to the former as well. The gill-slit next behind (between 

 the hvoid arch and the first branchial arch ])ro]iei') has 

 its branchial lamelke set in a large. Init single, arcuate 

 row on the inside of the operculum, throughout the 

 hind margin thereof, as well as on the inside of the 

 plates situated below the operculum and corresponding 



firmh loalescent with the hind wall of the branchial 

 cavit\- or anterior side of the scapular arch. 



In an adult state the mouth of the Sturgeons is 

 entirelv toothless; but their larva- have teeth, in form 

 ;ind distribution not unlike those of the Sharks, in their 

 corneous structure resembling those of the Lampreys, 

 both in the u])per and lower jaws and on the cerato- 

 branchial bone (<:hi\) of the first branchial arch proper. 

 These teeth are developed soon after the palato-Uiandi- 

 bular arch, originally continuous and arcuate, has brok- 



» Abh. Akad. Wiss. Berlin 1844, p. 133, taf. II, fig. 1 and taf. V, fig. (!. 



