324 MR. W. K. PARKER ON THE OSTEOLOGY OF BAL^NICEPS REX. 



The cervical vertebipe of the Balseniceps are relatively stronger and shorter than 

 those of the great Adjutant, whilst they form a remarkable contrast to those of the 

 Heron — a bird which not only has more of these joints than its relations, but in which 

 the individual vertebrae are exceedingly long and narrow. The difference between the 

 structure of the neck in the typical Heron and in the Balceniceps is remarkably like 

 what we see in the Mammalia, when we contrast the cervical vertebrse of the Vicugna 

 with those of some large Stag, such as the Wapiti, or the Sambur Deer. The large, 

 broad, spoon-shaped jaws and the flat head of the Boat-bill require a shorter neck and 

 individually shorter vertebrae than those of the Heron with its long narrow cranium, 

 and its narrow, straight, tapering, pointed mandibles. 



Yet in nothing but in the decrease of number and the shortening of each joint do 

 the cervical vertebrae of Cancroma differ from those of Ardea ; whilst all the change 

 that has taken place between those of Balcsniceps and Cancroma is that in the former 

 two vertebrae have been added, and the relative as well as real strength of each bone 

 greatly increased. 



Atlas. (PI. LXVI. figs. 1, 3, 4 at.) 



The atlas is small, as in all birds, and its ' proccelian' cup for the articular condyle 

 of the occipital bone is large in proportion. This cup is imperfect, a large crescentic 

 piece being cut away, as it were, from the top, to make room for the 'odontoid' pro- 

 cess, which process, although ossified to the axis, in reality belongs to the atlas, being 

 the internal or ' diaphysial ' part of its centrum. Behind where the upper edge of the 

 cup is cut away, there are two small articular facets of a semi-elliptical shape for arti- 

 culation with the sides of the tip of the odontoid process. In Balceniceps and its allies 

 there are no foramina for the vertebral arteries on the sides of the atlas. The post-zyg- 

 apophyses of the atlas send backwards a rather broad triangular process for muscular 

 attachment : these are obsolete in Cancroma and the Small-headed Heron ; but they 

 are largest in the Adjutant, in which bird they divaricate outwards. The posterior 

 articular surface of the centrum of the atlas is of the usual U-shape, and the inferior 

 surface is marked in its latter half by one mesial and a pair of lateral tubercles. The 

 upper concave aspect of the centrum is full of small pneumatic holes. 



Note. — In the Woodpecker and other arboreal birds, the cup of the atlas has a 

 very perfect rim, but it is perforated below for the passage of the odontoid ligament ; 

 here also the vertebral arteries are bridged over. In the young Emeu the lower or 

 'hypophysial' part of the atlas is distinct from the neural arch as well as from its 

 odontoid element. Query, does not this part of the Bird's centrum answer to the 

 marginal parapophyses of the abdominal vertebrae of the Fish, as well as to the mesial 

 hypapophyses of the Vertebrata generally ? 



It is not ep.sy to draw a line between these processes or elements (which are so 

 seldom autogenous), and to say where one begins and the other ends; at any rate the 

 lateral processes of the base of the atlas are the homotypes of the parapophyses of the 

 succeeding vertebrae, whilst the mesial tubercle is a rudimentary ' hypapophysis.' 



