636 
SCANDINAVIAN FISHES. 
ryngeal bones) on each side. Another character of more 
general validity — which indicates the low rank of these 
fishes among the Teleosts — is the imperfect ramifica- 
tion and, in some cases, the defective transverse divi- 
sion (articulation) of the soft fin-rays. 
The form of the body is very variable in the Hemi- 
brancliii. The Sticklebacks, which possess the ordinary, 
most typically piscine form, are so like the Horse- 
Mackerels that they have been ranged beside the latter 
by many systematists. All the others are of more 
singular form, elongated like the Garpikes or laterally 
compressed, and all with the head prolonged into a long, 
tubular or conical snout, at the end of which the small 
mouth is situated. This prolongation, however, does 
not depend here, as in the Garpikes, on the elongation 
of the jaws, but corresponds more exactly to the struc- 
ture we have remarked above in certain Plectognates, 
here affecting the ethmoid bone, the three pairs of 
pterygoid bones, the preoperculum, and the interoper- 
culum, which together form the greater part of the 
long rostral tube, special suborbital bones, on the other 
Fig. 157. Gasterosteus aculeatus, tracliurus , natural size. From 
Eckernforde Bay. A: from the side; B: from above; C: ventral and 
anal regions; ds, dorsal plates; vs, plate of the ventral fin (pelvic 
hone), in A its ascending lateral process; a, vent; at, anal spine; 
vt, ventral spine. After Heincke. 
i. 1. 2 . 
Fig. 156. Shoulder-girdle of Gasterosteus aculeatus; magn. 9 or 1 0 diam.; after Parker. 
A: Bones of the left side, seen from without, pt, posttemporal bone (Ganoid plate of the first dermal ring); 1.1.2, first lateral plate (Ganoid 
plate of the second dermal ring); 1.1.5, fourth lateral plate; cl, clavicles; sc, scapula; sc./, scapular fenestra; b.l , first basal bone of 
the pectoral fin; b.4, fourth basal bone; p.cr, ossified part of the coracoid bone (praecoracoideum, according to Parker); i.cl, inter- 
clavicles. 
B: Section of the lower part of the clavicular arch, to show the cartilaginous part of the coracoid bones (e.cr, epicoracoideum, according to 
Parker) between the clavicles. 
C: Interclavicles, seen from the ventral side, with the anterior end up. 
