STURGEON -F I S HES . 
1 05 1 
Of the system of the lateral line (dermal sense- 
organs) we find in young Sturgeons pores in the plates 
of the lateral line and in the temporal and mastoid 
plates, as well as a connecting canal (a junction com- 
mon in the Teleosts too between the two supratemporal 
canals, cf. S])t in tig. 104, p. 368) across the occiput, 
between the mastoid and supraoccipital plates. On each 
side of the head the main canal runs forward under 
the squamosal plate, to branch at the upper posterior 
corner of the eye downwards to the sphenotic and post- 
orbital plates, and forwards, under the inner margin 
of the supraorbital and ectethmoidal plates, in the der- 
mal bridge between the nostrils. The system is most 
distinct, however, on the snout, especially on the under 
surface thereof, where the four filaments of touch (bar- 
bels) of the Sturgeon a, re also situated. Here we find 
partly small, simple pores (ordinary lateral line pores), 
partly agglomerations of these, forming wheel-shaped 
figures that cover large muciferous cavities. These ca- 
vities (the ScMeimsdcke or Nervensdcke and Gallert- 
rohren of Leydig, the tubes muceux a ampoules of Du- 
meril) occur in the common Sturgeon, being most 
distinct in young specimens, 1) below 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, sometimes throughout its extent. 
The small, simple 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 each sub- 
orbital plate, and thus answering to the suborbital 
branch of the Teleosts, but running forwards, outside 
the outermost barbel, and discernible in young speci- 
mens to the very tip of the snout. 
The variations in the form and arrangement of the 
body bucklers belong to the description of the several 
species; but common to all the Sturgeon-fishes and 
most of the Ganoids are the so-called fulcra , imbricated 
splints, resembling spinous rays, at the anterior mar- 
gins of the vertical fins. The posterior 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. The fins of the Sturgeon-fishes 
a.re furnished, like those of the Teleosts, with secondary, 
partially ossified and sagittally (in the longitudinal di- 
rection of the body) divided rays, originally all simple 
and articulated. But with age these rays become more 
and more confluent and, in the anterior part of the 
fins, hardened, as in most of the Physostoms, so that 
the foremost rays are spine-like, though with distinct 
vestiges of the original articulations. 
In the internal structure of the Sturgeon-fishes we 
have already remarked the most essential respect where- 
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 abdominal cavity is about 700 mm. The 
thick-walled oesophagus runs in this specimen for a 
distance of about 9 cm. close under the spinal column, 
and is internally furnished here anteriorly with 5, poste- 
riorly with 8 series of hamate or (behind) valvular 
flaps, exchanged furthest back for shallow, flat folds 
of the mucous membrane. Where these folds terminate, 
the mucous membrane of the stomach, which is some- 
what wider, but has thinner walls, commences, and 
about 4 cm. further back opens the short, but wide, 
pneumatic duct of the large and thick-walled air-bladder. 
Fig. 290. Transverse section of the anterior part of the spinal co- 
lumn in Acipenser ruthenus. After Wiedershkim. 
Ps , upper spinous process; El , elastic tendinous band; N, neurapo- 
physis; SI, fibrillar tissue (belonging to the skeletogenous layer); 
M, medulla; P, inner membrane (phi) of the myelon; Ic, intercalare; 
C, notochord; Os, inner chordal sheath; Ee, outer (elastic) chordal 
sheath; H, hsemapophysis; Z, basal part of a haemal arch; Fo , cross- 
pieces projecting mediad (inwards), and ventrally (interiorly) covering 
the main trunk of the arterial system (aorta, Ao). 
The stomach now assumes a more intestine-like form, 
and runs upwards to the left, to a distance of about 
23 cm. from the diaphragm, where it turns forwards 
to the right and downwards, to a point (tig. 291, v) 
distant about 3 cm. from the diaphragm, where it 
again bends back and is thickened. At each crook its 
inner surface is furnished with thick, terete folds of 
the mucous membrane, 8 at the former bend, 6 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- 
