1072 
SCANDINAVIAN FISHES. 
cartilage, which is directed from the tip of the rostral 
cartilage (B) to the roof of the nasal capsule on the 
same side. These two lateral cartilages and the rostral 
cartilage thus build up a three-sided pyramidiform case, 
within which is enclosed the fibrous capsule wherein 
the ampullai hereafter to be described have their caecal 
base. In the Holocephali — where, as in the generality 
of deep-sea fishes, the rostral system of the lateral line 
is particularly well developed — the soft snout and the 
said capsule are supported by a pair (fig. 294, lr 2 ) of 
cartilaginous rods, widely separated at the bases but 
converging towards the tips, with the liases resting on 
the snout in front of the nasal capsules, and by an 
The morphological homologues of the jawbones of 
the Teleosts and the higher vertebrates also appear in 
the Elasmobranchs under the guise of labial cartilages. 
The Elasmobranchs are in general raptorial fishes of a 
pronounced type, with powerful teeth in the mouth; but 
these teeth are set, not on the jawbones proper, but 
on the predecessors, in the development of the verteb- 
rate type, of the palate and lower jaw, on the palato- 
quadrate cartilage (figs. 294 and 298, qpg) and the 
so-called Meckelian cartilage (MU) of each side, the 
predecessors of the lower jaw, which cartilages appear 
even in the embryos of the highest vertebrates as gra- 
dually evanescent rudiments in the structure of the 
Fig. 299. Skull of a Tope ( Galeorhinus ), seen from the left ( A ) and from above ( B ). After Gegenbaur. 
cro, rudiment of occipital crest; fonpf , prefrontal fontanelle; ie, incisura etlimoidalis. The other letters are explained in the preceding figure. 
unpaired, thicker and firmer cartilaginous rod (by), set 
on the bridge of the snout between the two anterior 
openings of the ethmoidal canal (ce), a confluence of 
the anterior parts of the preorbital (cp) and orbitonasal 
(on) canals. The males also possess a similar carti- 
laginous rod (If) above the preorbital process, free and 
mobile, transformed to a, prehensile organ set with 
teeth, and probably serving to hold the female during 
copulation. The history of evolution has not yet elu- 
cidated the morphological significance of these carti- 
laginous rods in the Holocephali , but from this point 
of view they should probably be ranged, one and all, 
beside the labial cartilages of the Sharks. 
mandible. The relation of the palatoquadrate cartilage 
to the skull we have already considered. At the pos- 
terior (quadrate) extremity it articulates with the 
Meckelian cartilage, which here functionates as a lower 
jaw, so that the two pairs of cartilages form a ring 
around the gape. But these cartilages, especially the 
Meckelian, are closely united .behind by ligaments to 
the hyoid arch, an opening (the spiracle, fig. 298, spit) 
being left, however, between the quadrate (qpg) and 
the hyomandibular (hm) cartilages, and the anterior 
margin of this spiracular canal being furnished either 
with a more or less developed cartilaginous disk (spc), 
answering to the metapterygoid hone of the Teleosts, 
