Page 339. 
338 ON THE ANATOMY OF PLOTUS ANHINGA. 
vertebra, and gives off slips, on its way up, to the serially homologous 
processes of the 9th and 10th vertebra. A similar tendinous slip to 
the 11th vertebra has an independent origin from the bodies of the 
15th and 16th vertebra, internal to the main muscular mass, which is 
almost the size of a lemon, and with its fellow of the opposite side, of 
much the same shape, filling up and projecting beyond the slight ante- 
rior concavity above mentioned, formed by the mutual articulations of 
the 15th, 16th, 17th, 18th, and 19th cervical vertebre. (In Plate 
[18] XXVI. figs. 1 and 2, these different details are clearly shown.) 
Posterior cervical region.—Here is an exaggerated development of 
muscle in the juxta-thoracic part, opposite the similar enlargement in 
front, although it is not so considerable behind. The longus colli pos- 
terior is the muscle which is excessively developed. It becomes dif- 
ferentiated from the posterior dorso-spinal mass opposite the 14th and 
15th cervical vertebree to run up the neck in the form of a fleshy 
belly which receives additional origins, in the form of muscular slips, 
from the vertebre as high as the 9th cervical. Where the slip from 
the 10th vertebra (which is a small one) joins it, the muscle becomes 
tendinous, forming a rounded cord, to the inner side of which the | 
large fasciculus from the 9th vertebra is attached. 
A reference to the account given above of the disposition of the 
vertebra in this region will make it evident that the tendon of the 
longus colli posterior must make a considerable backward turn opposite 
the transverse line of articulation between the 8th and 9th cervicals 
—hbecause there the two bones meet at a considerable angle, with 
the genu directed forwards. This being the case, some special mecha- 
nism is essential to prevent the tendon from breaking away from the 
vertebral column when the muscle with which it is associated contracts. 
In fact, a pulley has to be formed round which the tendon may turn 
in the same manner that at the knee, in birds, the biceps crwris is able 
to act upon the fibula from a point situated some way down it, because 
it is bound closely to the greatly bent knee-joint by the well-known 
sling-band in that region. In Plate [18] X XVI. figs. 1 and 2, the sling- 
band here described is clearly shown. 
A similar sling-band is found in the posterior cervical region of 
those birds which have any great backward curve of the neck, it in the 
Gannets being also associated with the 9th vertebra. It is nothing 
more than a specialization and strengthening of the aponeurosis which 
is always found covering the muscles, opposite the place where the 
strain occurs. In Phalacrocorax carbo the general sheath is strong, 
and no specialized band can be distinguished. s 
In Plotus anhinga this sling-band is attached at its inner end, with 
its fellow of the opposite side, to the middle line of the posterior 
surface of the neural arch of the 9th vertebra, about half-way between 
