STURGEON-i'ISIIES. 
1047 
place is occupied in the skull of the Teleosts (see, for 
instance, the cranium of the Eel, p. 1014, tig. 268, B , 
par) by the parietals ( parietal scutes , tig. 286, par). 
Their hind extremities are parted by the said project- 
ing lobe of the supraoccipital scute; they are sometimes 
contiguous throughout the rest of their length (tig. 286, 
B), and in other cases their anterior ends are separated 
(tig. 286, A) by an osseous plate (et) fitting in between 
them from in front. Before them and partly on the 
sides of their anterior extremities lie a pair of plates 
( frontal scutes, fr), often but slightly inferior to them 
A 
smaller plates. All these variations may be observed 
in the same species, e. g. in the common Sturgeon. 
The inconstancy of form depends upon the comparatively 
lax connexion between these scutes and the skeleton, 
the looseness increasing towards the snout, which is gene- 
rally covered with numerous, more irregular, smaller 
plates, except on the sides, which are armoured in adult 
specimens of the common Sturgeon with large scutes in 
a definite row. Outside each parietal plate lies a squa- 
mosal scute (by others called the temporal scute, squ), 
and in front of this, above the orbit, on the outside ot 
Fig. 286. Upper surface of the head iu the Sturgeon (Acipenser sturio). of the natural size. Two figures showing variations iri this 
species; both specimens taken at Christianstad. 
dy, first dorsal scute; et, ethmoidal scute; ett, ectethmoidal scute; fr, frontal scute; mt , mastoid scute; n, anterior nostril; o, eye; ocs, occi- 
pital scute; par, parietal scute; ptob, postorbital scute; ptp, posttemporal scute; spho, sphenotic scute; spo, supraorbital scute; spir, spiracle; 
squ, squamosal scute; tp, temporal scute; op, operculum. 
in size. These correspond in situation to the frontal 
bones of the Teleosteous skull, and are sometimes close- 
ly applied to each other, but usually separated at least 
in front (fig. 286, B), sometimes throughout their length 
(fig. 286, A), either by an elongated ethmoidal scute (et), 
which may even extend, as mentioned above, between 
the anterior extremities of the parietal scutes, or by 
several (up to 5 or more and sometimes two-rowed) 
each frontal plate, a curved row of three scutes, the 
posterior representing a postfrontal bone ( sphenotic scute, 
spho), the anterior a prefrontal bone ( ectethmoidal scute, 
etl), and the middle one a supraorbital bone ( supra- 
orbital scute , spo). The lower end of the sphenotic scute 
touches the top of an angular plate, the form of which 
calls to mind the preoperculum of the Teleosts, but 
which here composes the posterior and inferior limits 
Scandinavian Fishes. 
132 
