354 PKOF. ST. GEOKGE MIVART ON THE 



The whole axial skeleton, when compared with those of the genera previously 

 described, presents a remarkable contrast in the great prolongation of its more preaxial 

 part, while its pelvic part is somewhat shortened, notably as compared with the same 

 part in Phalacrocorax, with which genus, nevertheless, the axial skeleton of Plotus, on 

 the whole, most agrees. Thus it agrees with Phalacrocorax in the strongly opistho- 

 crelous condition of the trunk-vertebrae, and in their median, subcentral, laterally 

 compressed prominences, though (as we shall see) they have not the same nature as 

 the analogous parts in Phalacrocorax. 



In the elongation of the anterior cervical vertebrae Plotus is more nearly approached 

 by Pelecanus; but these bones are not nearly so long and slender relatively in the 

 last-named genus, nor are they so smooth dorsally and with such rudimentary neural 

 spines as in Plotus. 



THK CERVICAL VERTEBRA. 



These vertebrae, from their length and the little relative prominence of their pro- 

 cesses, resemble (as has just been said) the cervical vertebrae of Pelecanus ; but in 

 number and essential details of structure they rather resemble those of Phalacrocorax, 

 presenting at the same time a number of special peculiarities. 



As has been pointed out by Professor Garrod 1 the vertebrae are mostly long to the 

 eighth, which is extraordinarily elongated (as also the third, fourth, and fifth), and 

 forms an angle open ventrad with its predecessor, and an angle open dorsad with its 

 successor. 



The styloid rib-like processes are little developed in the first seven vertebrae, but in 

 the eighth and succeeding ones much so, above all in the eighth, where their length is 

 such as to extend peculiarly, ventrad, and postaxiad of the preaxial end of the haemal 

 arch of the vertebra next behind, i. e. the ninth. 



The ATLAS is much like that of Phalacrocorax ; but there are no lateral hypapophysial 

 processes, and the hyperapophyses project less postaxiad, scarcely more so than in 

 Pelecanus. The odontoid foramen is smaller, relatively as well as absolutely, than 

 in any of the three preceding genera (Plate LVIII. figs. 1 & 2). 



The AXIS differs remarkably from that of all the three preceding genera in its great 

 relative antero-posterior length and little dorso-ventral extent, due principally to the 

 small development of the hypapophysial element; it is also relatively less broad 

 transversely (Plate LVIII. figs. 3 & 4). 



The odontoid process is very small. There is a distinct, elongated, though low, neural 

 spine. The articular surfaces of the postzygapophyses project as much postaxiad as do 

 the zygapophyses themselves. There is an interzygapophysial ridge. The postaxial 

 articular surface of centrum looks dorsad as well as postaxiad ; and its ventral margin is 

 strongly concave. The ventral surface of the centrum presents three antero-posterior 



1 Proc. Zool. Soc. 187C, p. 33&-T. 



