1074 
SCANDINAVIAN FISHES. 
Avas shown by Hannover to be the same as that of 
(the teeth and) the dermal spines. 
Among the peculiarities of the internal organs in 
the Elasmobranchs we have already considered the 
structure and position of the heart. A further charac- 
vity; and as the latter, being pierced by the abdominal 
(anal) pores, one on each side of the anal aperture, is 
in a certain degree open to the surrounding water, this 
element may find a passage to the heart itself®. The 
intestinal canal is comparatively simple (tig. 301). The 
phh\ 
tv mpt opt pob 
Fig. 300. Skull of a Thornbaek ( Raja clavatd) seen from above (A) and from the right (B). Natural size. After Parker. 
ehy , epihyoid; fa , foramen for the nervus facialis; fonf , frontal fontanelle; fonpf, prefrontal fontanelle; hhy, hypohyoid; nipt , metapterygoid; 
pob , preorbital; sthy, stylohyoid. The other letters are explained in fig. 298. 
teristic of these tishes is the communication afforded 
to the pericardial cavity by means of ttvo holes behind, 
in the diaphragm, Avith the abdominal (peritoneal) ca- 
Avide, but sometimes very short oesophagus ( d ) passes 
into a stomach ( e ) usually of greater length, and this 
terminates behind in a more or less prolongated blind 
a Monro, Struct., Physiol. Fish., Edinburgh, 1785, p, 20, pi. II, 22, 23, pi. XVIII, 10, 11, 12. Blainville, Ann. Mus. Hist. Nat., 
tome XVIII (1811), p. 111. 
