AXIAL SKELETON OF THE PELECANID^. 853 



The Sternum. 



The sternum (Plate LXI. figs. 3 & 4) is shorter and broader than in Sula, with the 

 proportions of Pelecanus, but less contracting, laterally, postaxiad. The clavicles are 

 not ankylosed to it. 



The keel extends much relatively as in Pelecanus ; and the coracoid grooves form'an 

 angle much as in that genus, and therefore a less acute one than in Sula. The median 

 xiphoid [mx) agrees with that of Sula in not extending postaxiad as much as the lateral 

 xiphoids do, thus differing from Pelecanus. These lateral xiphoids are obtusely pointed, 

 not spatulate {Ix). 



The pleurosteon may have only four elongated articular processes in Ph. carho, but 

 generally has five such in other species. 



The concavity and convexity of the sternal osseous sheet is much as in Pelecanus, 

 and not flattened as in Sula, though the middle part of the postaxial portion of its 

 ventral surface is not so convex transversely as in Pelecanus. 



The articular surface behind the coracoid groove is not so broad relatively as either 

 in Sula or Pelecanus. 



A process may spring preaxiad from dorsal end of concave dorso-preaxial margin 

 of keel. 



PLOTUS. 



The anatomy of Plotus has been recently described by Professor Garrod, in a very 

 interesting and instructive memoir in the 'Proceedings' of the Zoological Society 

 for 1876, p. 335, pis. 26 to 28. Its skeleton was noticed by Mr. Eyton in his 

 ' Osteologia Avium,' p. 218 ; and by W. Donitz (as concerns the cervical vertebrae) 

 in the 'Archiv fiir Anatomie und Physiologie,' 1878, p. 357, plate ix. a. 



It has been described with much detail by Brandt, who has given figures of the entire 

 skeleton, the pelvis, and sternum, in the ' Memoires de I'Academie des Sciences de 

 St.-Petersbourg,' 6"°^ serie, Sciences Mathematiques, Physiques et Naturelles, tome v. 

 seconde partie, Sciences Naturelles, tome iii. 1840, p. 132, pi. 4. 



I have myself examined a skeleton of Plotus anhinga in my own collection, and also 

 another and a skeleton of P. novce-hollandice, both in the Museum of the Royal College 

 of Surgeons. 



The total number of vertebrse seems to be 45 or 46, without counting the pygostyle. 



These vertebrae are subdivisible as follows — 18 cervical vertebrae (in the specimen 

 of P. novce-hollandice there are only 17 ; but this is probably owing to one vertebra, 

 the 15th, having been lost), 2 cervico-dorsal, 5 or 6 dorsal (in one specimen of P. 

 anhinga there are but 5), 4 lumbar, 2 or 3 lumbo-sacral, 2 sacral, 4 sacro-caudal, and 

 7 or 8 caudal vertebrae. 



