426 PROCEEDINGS OF THE CANADIAN INSTITUTE, 
_ 
The latter divides and sends a branch backwards and another for- 
wards along the outer dorsal surface of the mandible. 
The A. carotes tnterna (Pl. VIII. Fig. 1, c. in.) arises from the 
anterior surface of the first branchial vein close to the carotis externa, 
and passes forwards along the side of the skull. A short distance from 
its origin it thickens into a gland-like structure (ps) nearly 8 mm. long 
and 3 mm. wide in the middle and tapering towards both ends. This 
organ is exposed from the roof of the mouth by dissecting away the 
adductor arcus palatini from its attachment to the side of the skull. 
From this surface (ventral) the channel of the artery is distinctly 
seen passing directly through it from end to end Transverse sec- 
tions show that the wall of the vessel is thickly perforated throughout 
the length of the organ by small openings of vessel-like passages 
(Fig. 2, 5), which are quickly lost in the fine interspaces of the con- 
nective tissue of which the thickening is formed. Scattered through 
it are seen the small arteries by which the blood is again collected 
from the interspaces (Fig. 3, a). An examination of the position and 
relations of this structure leaves no doubt but that it is the remains 
of the psewdobranchia which has become reduced to a mere rete 
mirabile. It is worthy of note in connection with its reduced state 
in Amiurus, that Owen mentions Stlurws as one of those fish in 
which it is entirely absent. That it is the pseudobranchia is shown 
by the fact that the arteria ophthalmica magna (Fig. 1 a. 0. m,) arises 
from its anterior dorsal surface which is in contact with the optic 
nerve, in company with which the artery passes to the eye. 
Three small arteries arise from the same surface, posterior and 
medial to the former, and immediately enter the braincase. These 
are the encephalic arteries, and their origin from the pseudobranchia 
is unknown among other 7'eleostei.' In this point, however, as also 
in the structure of the organ Amurus shows a singular agreement 
with Acipenser.” 
As far as I am aware the pseudobranchia has not the peculiar 
direct relation to the carotid, described above, in any other fish, but 
is situated upon a branch of that vessel even in the sturgeon. 
The internal carotid supplies the adductor arcus palatini, a branch 
to the posterior part arising behind, and those to anterior part after 
1 Dr. F. Maurer—Ein Beitrag z. Kennt. d. Pseudobranchien d. Kuochenfische. Morph. 
ahrb. Bd. IX. Taf. XI. 
Owen—l. c. Vol. I. p. 489. 
