516 MULLER ON THE STRUCTURE OF THE GANOIDS, 
stomach has no blind pouch, the pyloric portion forms an un- 
limited number of curves, and after a muscular swelling con- 
stitutes the pylorus. The duodenal loop comes next; this receives 
the terminations of the appendices, the biliary duct, and the 
duct of the glandular pancreas discovered by Alessandrini; 
the lower extremity of this forms another valve, from the cir- 
cumference of which the spiral valve of the valvular intestine 
takes its origin. The Rays form the transition from Polypterus 
to the Sturgeons; their bursa Entiana is prolonged towards the 
pylorus in the form ofa retort-like canal, so that the pylorus 
does not open into the body of the dursa, but projects into the 
neck of the retort. 
The brain of the Ganoidei is peculiar, and differs from that 
of the osseous fishes and Plagiostomi. That of the Sturgeons 
is well known from the ‘treatise by Stannius. I shall now 
give a short account of the brain of Polypterus. It resembles 
that of the Sturgeon, and consists, at its posterior part, of a 
very elongated medulla with the long sinus rhombicus, a cere- 
bellum, and comparatively small optic lobes, which terminate 
with a superior aperture in the lobus ventricul tertii. Next fol- 
low the very large and deeply-divided hemispheres, and not 
olfactory lobes, as I called them in the Jahresbericht. The 
brain is continued beneath them in the form of the olfactory 
lobes and the olfactory nerves. The decussation of the optic 
nerves found in osseous fishes is wanting; they do not pass over 
each other in an isolated state, but are united and form a chiasma 
as in the Sturgeon. The skull of Polypterus has a very con- 
siderable mass of cartilage beneath the bony coating, which partly 
incloses the auditory apparatus on each side, so that the latter 
is somewhat more covered than in the osseous fishes, which 
again reminds us of the Sturgeons. 
In the organs of sense, the Ganoids partly approximate to the 
osseous fishes, partly to the Plagiostomi. They have, like the 
Sturgeons, double nasal cavities, which do not occur in the Pla- 
giostomi. The processus falciformis and the choroid glands ap- 
pear to be wanting in Polypterus. 
The skin of the Ganoids may either be covered with rhomboidal 
or round enamelled scales, it may bear plates, or be perfectly 
naked. The Spatularie are naked sturgeons, their intestines 
and vertebral column are the same; the imperceptible transition 
of the Sturgeons to the Ganoids generally is easily recognised, 
