1090 
SCANDINAVIAN FISHES. 
than in other fishes. Four kinds of organs belonging 
to this system may also be distinguished: 1) the true 
lateral line with its ramifications on the head, the 
trunk, the pectoral fins, and the tail; 2) the so-called 
Lorenzinian ampul lm (muciferous sac ducts); 3) the so- 
called Savian vesicles; 4) the so-called pit organs. 
The lateral line, the histological structure of which 
has been elucidated by Leydig (fig. 307), has nume- 
rous ramifications, and opens on the surface of the body 
not only into simple pores, but also into long trans- 
verse branches originating at right angles or obliquely 
from the line itself and its ramifications. The main 
branches of the system indeed find their parallels in 
the ramifications we have seen above in the Chimsera; 
but peculiar to the true lateral line of the Rays is the 
complex network of canals on the pectoral fins. In the 
genus Baja we recognise on the upper surface of the 
head the transverse occipital (supratemporal or aural) 
branch (fig. 308, 21), the frontorostral branch with its 
divisions, the occipital (20 to l) and the supraorbital 
d b 
Fig. 307. Part of a branch of the cephalic system of the lateral line 
in the Thornback ( Raja clavata). Magnified. After Leydig. 
a, outer wall of hard membrane, removed on one side to show b, 
the inner, soft membrane, on which are visible the papillae (c) and 
the nerve centra (sensory spots, d), with extended ramifications of 
the entering nerves (e). 
(1 to 2), and the suborbital branch (7 to 8), which 
runs on each side of the body between the eye and the 
spiracle. When these branches have advanced nearly 
to the margin of the body (at 2 and 6’), the former 
quite close to the tip of the snout (2), the latter some- 
what further back (8), they pierce the body to reappear 
on the under surface of the head (2 to 6 and 8 to 11), 
and join each other as in the Chimaera. This junction 
is simple, however, in the said species and follows the 
median line of the snout (median canal, Garman); here 
it is double, one branch on each side of the median 
line, and the immediate continuation of the frontorostral 
branch (supraorbital division) bends outwards on the 
under surface of the snout in a sharp crook (from 3 
to 4 and 5). After the junction the suborbital branch 
is continued backwards by a maxillary part (6 to 9), 
that bends inwards, in about a line with the middle 
of the length of the nasal valvule, to a naso-maxillo- 
rostral branch (9), which indeed (at 10) joins the cor- 
responding branch of the other side to form a ma-xillo- 
nasal canal, but also sends out a maxillo-rostral canal, 
straight to the tip of the snout, within the continua- 
tion of the supraorbital branch on the under surface 
of the snout. The posterior and more immediate back- 
ward continuation of the suborbital branch and its ma- 
xillary part answers to the opercular canal of the Chi- 
maera, and has been named by Ewart the hyomandi- 
bular branch (12 to 19). This branch runs here (12 
to 13) on the outside of the branchial apertures (aphj, 
following the direction of the series formed by the 
latter, and on the under surface of the pectoral fin 
bends in a great loop, first backwards and outwards 
(13 to 14), then almost straight forwards (14 to 15), 
to a point near its origin, where it bends inwards (15 
to 16) and afterwards runs forwards (16 to 17), pa- 
rallel to its commencement and to the suborbital branch, 
until (at 17) it comes in a line with the nostrils, where 
it turns upwards straight through the body. On the 
dorsal side it now bends straight back (from 17 to 18), 
and after an inward curve (at 18), where it receives 
connecting ducts from the suborbital branch, it pursues 
its course along the margin of the pectoral fin, and in 
the posterior part of the dorsal side thereof (at 19) 
joins a pleural branch (22 to 23) from the lateral line 
proper. The last-mentioned part of the system follows 
on each side of the body the same course as in the 
Teleosts, from the temporal region (at 21) to the tip 
of the tail. At the shoulder- girdle it forms an outward 
bend and here it gives off on the dorsal side of the 
pectoral fin both the anterior pleural branch which we 
have noticed above at its junction with the termination 
of the hyomandibular branch, and, in the genus Baja 
and its nearest relatives, a posterior pleural branch 
(24 to 25), which ramifies in the posterior part of the 
pectoral fin. Just behind the mouth there lies, as a 
detached portion of the hyomandibular branch, a trans- 
verse canal (27), answering to the mandibular branch 
of the Chimsera. 
The ampullary system (fig. 309) properly belongs 
to the head alone, where all its canals have their csecal 
base. These organs have been known for more than 
three centuries", but their true nature was first eluci- 
Lorenzini, Observ. int. alle Torped ., 1678, and Munro, Struct., Physiol. Fish., 1785. 
