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Show 1876.] ANATOMY O F P L O T U S A N H I N G A . 337 with one another, more strongly marked than that between the 6th and 7th, and this, again, more decided than that between the 5th and 6th, and so on. The 8th and 9th vertebrae articulate so as to form an angle exactly the opposite in direction-namely, with its genu directed forwards instead of backwards. The same is the case with the 9th and 10th, the 10th and 11th, the 11th and 12th, the 12th and 13th; mote slightly so between the 13th and 14th, and the 14th and 15th ; whilst the 15th and following until the last (the 20th), which with the one above it carries imperfect ribs, form almost a straight line with one another, being slightly bowed, with the convexity directed backwards. With the exception of the atlas and the 6th and 7th, the cervical vertebrae are peculiarly elongate, the 8th being more so than the others, as may be seen in Plate X X V I . fig. 1. Donitz figures a pair of accessory bony bridges on the dorsal surface of the vertebra following the most lengthy one, which must evidently therefore be the 9th. He, however, speaks of it as the 8th, which seems to me to be an error depending on the omission of the consideration of the atlas, because in Plotus anhinga (both from Brandt's figure and my specimens) it is most certainly the 9th, as it is in Plotus novee-hollandice, Phalacrocorax carbo, and P. lugubris. I have, however, not seen Plotus levaillantii. Donitz attributes tbe peculiar kink in the neck of the Darters, which it is impossible to obliterate without lacerating the surrounding muscles, to the presence of the bony bridges he describes ; in this, however, he is mistaken, it depending on the above-mentioned peculiarity in the 8th cervical vertebra, by which it is angularly articulated with the 7th and 9th vertebrae, the upper genu being posterior, and the lower anterior. In further verification of this, it may be stated that in P. anhinga the bony bridges do not exist, and yet the kinking is most strongly marked. Myologically the cervical region of the Darter is very peculiar, on account of the great concentration of its muscular mechanism towards the thoracic end of that segment of the body, the tendons from them running lengthy courses up the neck. The anterior and the posterior cervical muscles will be considered separately. Anterior cervical region.-Normally in birds the longus colli anterior, or great front flexor muscle of the neck, commences as a series of thin tendinous slips from the middle of the bodies of the first two or three vertebrae which carry complete ribs (true dorsals). The fibres diverge and ascend in such a manner that they form a bilateral median mass acutely triangular at its lower end. They receive continual accessions from the bodies and haemapophyses of the cervical vertebrae, ending in slips which are attached, successively, to the apices of the anterior transverse processes three or four higher than the vertebrae whence they sprang. Through the whole length of the cervical region they are of very similar mass, and therefore help to maintain the otherwise fairly uniform diameter of the vertebral column*. * Vide Owen on Apteryx, Trans. Z. S. vol. iii. pl. 33, p. 310. PROC. ZOOL. Soc-1876, No. XXII. 22 |