1876.] ANATOMY OF PLOTUS AN'HINGA. 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; more 

 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 

 vertebras are peculiarly elongate, the 8th being more so than the 

 others, as may be seen in Plate XXVI. fig. 1. 



Donitz figures a pair of accessory bony bridges on the dorsal sur- 

 face of the vertebra following the most lengthy one, which must 

 evidently therefore be the 9th. Ue, however, speaks of it as the 

 8th, which s°ems 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 novoe-hollandice, Phalacrocorax cm-bo, and P. 

 lugubris. I have, however, not seen Plotus levaillanlii. 



Donitz attributes the peculiar kink in the neck of the Darters, 

 which it is impossible to obliterate without lacerating the surround- 

 ing 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 to- 

 wards 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 gi*eat 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, succes- 

 sively, 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. pi. 33, p. 310. 



Proc. Zool. Soc— 1876, No. XXII. 22 



