PEOFESSOE OWEN ON THE GENUS DINOENIS. 171 



in that vertebra. The postaxial surface is more definitely subquadrate, with the 

 angles rounded off and the upper and lower borders emarginate (fig. 34, j)c). The 

 transveree convexity is not greater than the vertical concavity ; both are feeble, so that 

 the entire surface approaches to flatness ; and in a duplicate homologue the flattening 

 is greater than in the specimen figured. In both the surface has lost its synovial 

 smoothness, through suppression of motion upon the first sacral vertebra. The trans- 

 verse dimension does not exceed, as it does in Struthio, the vertical one. 



The neural canal (fig. 34, n) is more depressed than in the twenty-first vertebra, and 

 still more deviates from the form shown by the hinder outlet in Mivart's figure 56 of 

 the Ostrich. The parapophysis in Dinornis (fig. 33, p) is represented merely by the 

 raised margin of the capitular concavity. The diapophysis is less massive in proportion 

 to the rest of the vertebra, and especially the neural spine, than in the antecedent 

 dorsal. The neural spine is not carinate along either the fore or the hind border ; both 

 present a flat rough surface, about two thirds the breadth of each smooth lateral 

 surface. A transverse section of the spine thus gives an oblong quadrate figure. A 

 pair of depressions at the fore part of the base of the spine intervene between it and the 

 prezygapophyses ; they answer to the ' antero-lateral fossae,' / ^, in Mivart's figures 55, 

 57. A narrower pair of fossse hold a like relation to the postzygapophyses, answering 

 to those marked/^ in figs. 56 & 67 ('Mivart'). The fossae,/-, ib. ib.,are feebly, if at 

 all, represented in Dinornis. 



The pleurapophysis retains its twofold articulation, but has lost in length ; its 

 hsemapophysis is attached to that of the preceding segment, and this element fails to 

 reach its spine (sternum) in the fifth and subsequent dorsals. 



The sternum may be considered, archetypally, as a coalescence of four or more such 

 haemal spines, the foremost retaining its connexions with its haemapophyses, which 

 are expanded in Struthio and in birds of flight as ' coracoids ;' but in Dinornis the 

 ' coracoids ' retain the slender proportions of the true thoracic haemapophyses. They 

 are also here confluent with their pleurapophyses, which, detached as a ' scapula ' from 

 its proper centrum, has the proximal end free without articular head, and in Dinornis 

 is reduced to the normal form of a rib with diminished proportions. 



Eetaining these views of the ' general homology ' of the sternum, I find its proper 

 place of description at the part of the axial skeleton here attained. 



The sternum belonging to the skeleton of Dinornis maximus under description has 

 suffered some mutilation ; but a detached example of the bone, transmitted from New 

 Zealand to Edinburgh (Plate XXXII.), shows a unique condition of integrity. 



StiU regarding, after long practice in the interpretation of a\ian fossils, the sternum 

 as one of the most characteristic and taxonomically instructive parts of the skeleton of 

 the bird, I append figures of the natural size of this most perfectly preserved specimen 

 of the bone, which is referable to the largest of the known species of Dinornis i. 



• This statement is made on the faith of the sternum transmitted with the rest of the skeleton of Dinornis 



VOL. X. — PABT III. No. 6. — October \st, 1877. 2 b 



