506 MULLER ON THE STRUCTURE OF THE GANOIDS, 
of this animal, and essentially contribute to its explanation, still 
they do not contain certain facts, which directly relate to the 
question of the nature of the Ganoidei, nor of their relations and 
limits, and the determination of which is the object of this trea- 
tise. Moreover, all we know of the internal structure of these 
two fishes is referable to generic peculiarities, which occur in 
one of them, but are absent in the other. The anatomical cha- 
racters of the Ganoidei are to be sought for in the structure of 
the heart, the blood-vessels, the respiratory organs, the sexual 
organs, the brain, and the organs of sense. 
The first point to which I shall draw attention is the struc- 
ture of the heart, or rather of the dulbus arteriosus. 
I have long attended to the importance, in a systematic point 
of view, of the internal structure of the arterial trunk arising 
from the heart. We know, that in those osseous fishes in which 
it has been examined, only two opposite valves are situated at 
the origin of the muscular bulb, between it and the cavity, 
whilst the higher cartilaginous fishes, the Sturgeons, Plagio- 
stomi (Rays and Sharks), and the Chimere, have three or more 
longitudinal rows of valves within the muscular bulb, the num- 
ber in each row varying from two to five according to the genus. 
At that spot, opposite which the two valves of the osseous fishes 
are found, the former fishes have no valves. 
The Cyclostomi are essentially different in this respect from 
both the higher cartilaginous and the osseous fishes. ‘They re- 
semble the osseous fishes in possessing only two opposite valves 
at the origin of the arterial trunk from the cavity, but they differ 
from both orders essentially by the muscular arterial bulb, or 
accessorial arterial heart being entirely absent. Their arterial 
trunk consists merely of the simple coats of the artery. This 
I found to be the case in both Petromyzon and Myzxine*. 
These distinctions appeared so constant in all osseous and car- 
tilaginous fishes which I have examined, that they seemed to 
indicate a fundamentally different disposition of the orders.. I 
am unacquainted with any character, either anatomical or zoo- - 
logical, which equals this in its absolute certainty. In fact, if 
the Ganoidei are essentially distinct as an order from other fish, 
a marked difference must occur in this part. 
* See Vergl. Anatom. der Myxinoid. 3 Forts, Abhandl. d. Akad. d. Wissen- 
schaft., J. 1839, p. 284; see also on the difference in the valves in the orders, 
families and genera, the note in Archiv f. Anat. u. Phys., 1842, p. 477. 
