nriiciKiiN-KisiiKs. 



lO.il 



Of the sxsti'iii of tlif iMtcviil line (dcriUMl si'iisi'- 

 orcnns) we find in xoiiny- Sturycoiis jKircs in tlic iilates 

 of tlu' lateral line and in tiie tenijioral and niastnid 

 nliiti's. as well as a eDniieeting eaiial (a innctimi <'()ni- 

 1111)11 in the Teleosts too between the tw(j supratemporal 

 canals, ef. s/if in fig. 104, p. i)(j8) across the ocei])Ut, 

 hetwoen the inastiiid and sii|ira(ieei])ital plates. < >n each 

 side of the head the main canal lains forward iiiiih'r 

 the s(|uaniosai [ilate, to hraiich a1 ihe upper pustei'idr 

 (•(iriiiT of the eye downwards to the spheiiotic and post- 

 urhital plates, and forwar<ls, under ihe inner margin 

 of the supraorhital and eclethmoidal plates, in the der- 

 mal bridge between the nosti-ils. The system is most 

 distinct, however, on tlu^ snout, especially on the under 

 surface thereof, Avhere the four filaments of touch (bar- 

 bels) of the Sturgeon are also situated. Here we find 

 partly small, simple pores (ordinary lateral line jjores), 

 parth' agglomerations of these, forming wheel-shaped 

 figures that cover large miiciferous cavities. These ca- 

 vities (the Si hlelmsih'li'r or Xrm'i/si'ickr and (rdllni- 

 riihri'ii of Lin dk;, the tiihfs ni/nrit.r ii iniipdide'^ fii' ]'>v- 

 MKJiii.) occur in the cmnnion Sturgeon, l>eing most 

 distinct in voung specimens, 1) lielow the eyes and on 

 the upper surface of the snout in a row along each 

 margin, forward from the nasal cavity, '2) on the under 

 surface of the snout, sinnetimes throughout its extent. 

 The small, sim])le pores are set on the under surface 

 of the snout in a single or double row, curving in- 

 wards from the lower posterior angle of eacdi suli- 

 nrhital plate, and thus answering to the suborbital 

 hraiich of the Teleosts, hut running forwards, outside 

 the outermost barbed, and discernible in voung speci- 

 iiieus to the ver\' tip of the snout. 



The variations in the form and arrangement of the 

 hoil\' bin Iders belong to the descriiition of the several 

 species; but common to all the Sturgeon-fishes and 

 most of the Ganoids are the so-called fnlrnt, imbricated 

 splints, resembling spinous rays, at the anterior mar- 

 gins of the vertical tins. The [josterior fulcra of the 

 .several fins, however, more and more assume the form 

 of true fin-rays, and thus clearly show a transition be- 

 tween these growths. Tlie tins of the Sturgeon-fishes 

 are furnished, lik(> those of the Teleosts, with secondary. 

 partially ossilied and sagittally (in the longitudinal di- 

 rection of the body) divided rays, originally all simple 

 and articulated. lUit with age these rays become more 

 and more confluent and, in the anterior ])art of the 

 tins, hardened, as in most of the Physostoms, so that 



the forcnnost ravs are spine-like, though with distinct 

 \estiges of the original articulations. 



In the internal structure of the Sturgeon-fishes we 

 lia\c alrea(l\- r(Miiarke(l the most essential respect wdiere- 

 in the heart differs from that of the Teleosts. In a 

 male Sturgeon measuring 1,845 mm. from the tip of 

 the snout to the end of the Upper caudal lobe, the 

 length of the ali(lominal casitv is about 700 mm. 'I'he 

 thick-Axalled oesophagus I'lins in this specimen for a, 

 distance of about M cm. (dose under tlie spinal c()himn, 

 and is interna 11\' furnished here anteriorly with .'), postc- 

 ri(u-l\ with H s(!ries of hamate or (behind) \alvular 

 flaps, excdiaiiged furthest back for shallow, fiat folds 

 of the mucous meinbraue. Where these folds terminate, 

 the muciius membrane of tlie stomach, wdiich is some- 

 what wider, but has thinn(!r walls, commences, atid 

 about 4 cm. further back opens the short, but wide, 

 piieiiniatic duct of the laroc and thick-\\alled air-bladder. 



I''ii;. "29U. Tr,insversi; siM-tioii of Ihe fiiilerior )uirl oi tlu- spinal cci- 

 luiiiii ill Acipoiscj' i-iilhtniis. .\flcr Wiedershkkm. 



y^s, upper spinous process; £/, elastic tenilinous band; A", ueurapo- 

 pliysis; <S7, tibrillar tissue (belonging to the skeletogenous laj'cr); 

 M, medulla; /-*, inner membrane (jrid) of the niyelon; /f, intercalare; 

 r. notochord; Us, inner chordal sheath; Ee, outer (elastic) chordal 

 sheath; H, hiemapophysis; Z, basal part of a hfemal arch; Fo, cross- 

 pieces projecting mediad (inwards), and ventrally (inferiorly) covering 

 the main trunk of the arterial system (aorta, Ao). 



'\\w. stomach now assumes a more intestine-like form, 

 and runs u])wards to tlie left, to a distance of about 

 28 cm. from the diajihragm. where it turns forwards 

 to the right and down\\ai-ds. t<i a point (tig. 291, ;•) 

 distant about '.\ cm. from the diaphragm, where it 

 agtiin bends back and is tliickened. At each crook its 

 inner surface is furnished with thick, terete folds of 

 the mucous membrane. 8 at the former bend, (i at the 

 Latter: but between these points the inside is smooth, 

 and the lasT-mentioned folds are continued on the inner 

 surface of the pylorus (pi/l). which is directed back- 



