ON THE ANATOMY OF PLOTUS ANHINGA. 339 
its proximal and distal extremities; whilst at its outer end it is fixed 
to the tubercle which is situated just outside the upper articular pro- 
cess of the same vertebra, a backward and slanting loop of tendinous 
tissue joining the two (vide Plate [18] XXVI. figs. 1 and 2). 
It is the ossification of this just-described tendinous loop which 
constitutes Donitz’s bridge in P. levaillantiit and P. nove-hollandie. 
In neither of the Society’s specimens.of P. anhinga, nor in that figured 
by Brandt, nor in a specimen of the same species seen by Donitz him- 
self, is this bridge ossified. It may therefore be that in P. anhinga it 
remains tendinous; or, less probably, it has happened that the four 
Specimens inspected have none of them been adult birds. One is at 
least 34 years old, we know. 
Through this bridge, as has been briefly described by Donitz, from 
a dried specimen, the tendon of the longus colli posterior passes—which 
it does before it receives the considerable fleshy fasciculus originating 
from the neural arch of the 9th vertebra, as is rendered evident in 
Plate [18] XXVI. figs. 1 and 2. 
The tendon, augmented by fibres from the just-mentioned additional 
origin, passes up the back of the neck, side by side with its fellow, to 
end by being inserted into the posterior surface of the lower articular 
process of the axis vertebra, it, in its course, sending small tendinous 
slips to the corresponding parts of the third and fourth cervical 
_vertebre. The tendon is peculiar in being ossified where it is opposite 
the bodies of the vertebre with which it is related, and supple at the 
joints, which makes it appear to be composed of alternate bony and 
fibrous elements when it is removed from the body. From the fifth, 
fourth, and third vertebre short muscular fibres ascend to join 
the corresponding portions of the main tendon in single penniform 
series. 
It is nearly always the case in avian anatomy that the inner fibres 
of the cervical portion of the longus colli posterior muscle become 
differentiated to form the digastrique du cou of Cuvier, better known 
to us as the biventer cervicis, a muscle one peculiarly interesting modi- Page 340. 
fication of which, in the genus Ceryle among the Alcedinidz, has been 
described and figured by Dr. Cunningham in the Society’s ‘“‘ Proceed- 
ings” *, This, by the way, I may mention, I have had the opportunity 
of fully verifying. Meckel, in his “ General Treatise on Comparative 
Anatomy,” tells usf that he found it at its minimum of development 
in the Galline, the Goose, and the Cormerant. In a specimen of Sula 
fusca, as well as in Phalacrocoraz carbo, it is present, but extremely 
small, I find. It is entirely absent in Plotus anhinga, the longus colli 
* “ Proceedings of the Zoological Soeiety,” 1870, p. 280. 
t+ French edition, Paris, 1829-30, vol. vi. p. 11. 
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