132 BULLETIN UNITED STATES GEOLOGICAL SUEVEY. [For. VI, 



transverse ellipse as we left it in the last cervical, in the vicinity 

 of the dorsal expansion of the myelon, to terminate nearly circular, and 

 much diminished in calibre, in the ultimate segment of the sacral ex- 

 tremity. 



The neural spines form by their interlocking a continuous ridge above. 

 The thickened crest of this ridge is produced by what we will call the 

 arrow-head joint, a true schindylesial articulation to be found in many 

 of the class. The superior margin of each spine becomes pointed ante- 

 riorly, extends forward, and is received into a fissure of the posteriorly 

 produced superior margin of the neural spine of the vertebra next be- 

 yond it. This arrangement has the appearance of so many little arrow- 

 heads placed in similar juxtaposition, and constitutes one of the elements 

 of stability of the dorsal vertebra in this bird. The open spaces remain- 

 ing among the bodies of the spines below, between their produced crests 

 and the several neural arches, are filled up by connecting ligament and 

 membrane. 



The diapophyses of the dorsals are a very much horizontally flattened 

 series. They are all slightly tilted upwards, the anterior ones being the 

 broadest and shortest, and the ultimate one, by a gradual departure in 

 this regard from the first, the narrowest and longest. In the middle of 

 the series, moderately well developed and antero-posteriorly produced 

 metapophysial ridges are found limiting the diapophyses externally; they 

 do not reach from one vertebra to another. The pneumatic foramina at 

 the bases of these processes are very minute and scarcely discernible 

 by the naked eye. 



The inferior diapophysial facettes for the x>leurapophysial tubercula 

 are concave-elliptical surfaces, with their major axes parallel to the 

 median line. The anterior ones are the more circular. 



The zygapophysial processes, to assist in the intimate proximity of 

 these vertebra, are short and thick. The anterior ones look upwards and 

 inwards, the reverse being the case with the posterior series, which lat- 

 ter develop pointed siDines that overlap above, each in its turn, on 

 either side, the vertebra next behind, at the base of the common neural 

 spine. The longer of these processes are found anteriorly ; they gradu- 

 ally disappear as we near the sacrum. 



The first dorsal hypapophysis consists of three plates, arising from the 

 centrum of the vertebra separately, and arranged as shown in Fig. 38. 

 On the second dorsal we find only a single quadrate plate in the median 

 plane, directed forwards. It occupies a position at the anterior margin 

 of the vertebra, but is produced posteriorly as a low, thin lamina of bone, 

 along the remainder of the centrum mesial to the raised and posterior 

 margin. The third vertebra takes it up in this form, and it is thus 

 passed along the series, constituting a continuous hypapophysial ridge, 

 intersected by the expanded anterior and posterior borders of the cen- 

 tra. 



The articular surfaces among the bodies retain their Ksual characters. 



