1876.] ANATOMY OF PLOTUS ANHINGA, 339 



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 bicej)s cruris is able to act upon the fibula from a point 

 situated some way down it, because it is bound close to the greatly 

 bent knee-joint by the well-known sling-band in that region. In 

 Plate XXVI. figs. 1 & 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 Grannets being also associated with the 9th vertebra. It is 

 nothing more than a specialization and strengthening of the aponeu- 

 rosis 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. 



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 halfway be- 

 tween its proximal and distal extremities ; whilst at its outer end it 

 is fixed to the tubercle which is situated just outside the upper arti- 

 cular process of the same vertebra, a backward and slanting loop of 

 tendinous tissue joining the two (vide Plate ^LXVI. figs. 1 & 2). 



It is the ossification of this just-described tendinous loop which 

 constitutes Donitz' s bridge in P. levaillantii and P. novre-hollandiae. 

 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 himself, 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 3-g- 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 ninth vertebra, as is rendered 

 evident in Plate XXVI. figs. 1 & 2. 



The tendon, augmented by fibres from the just-mentioned addi- 

 tional 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 vertebras. The tendon is peculiar in being ossified 

 where it is opposite the bodies of the vertebrae with which it is re- 

 lated, and supple at the joints, which makes it appear to be com- 

 posed of alternate bony and fibrous elements when it is removed from 

 the body. From the fifth, fourth, and third vertebrae 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 da cou of Cuvier, better known 

 to us as the biventer cei-vicis, a muscle one peculiarly interesting 



22* 



