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XII. On the Axial Skeleton of the Ostrich (Struthio camelus). 

 By St. George Mivart, F.R.8. 



Received June 18th, 1872. 



JtvECENT investigations having made it probable that the line of affinity between Birds 

 and ReptUes passes through the Struthious members of the first of these classes, I have 

 deemed it advisable to commence a study of the axial skeleton of the Sauropsida by a 

 detailed examination of that of the Ostrich, as of the most generalized type. 



By kind permission of the authorities of the Royal College of Surgeons, I have been 

 enabled to make use of the rich resources of that institution, not only for examination, 

 but for the purposes of illustration, aU the figures being from specimens in that 

 Museum. 



Bearing in mind the varying posture which the axial skeleton assumes in difierent 

 Sauropsidans, I think it better, generally, to employ the term precucial to denote that 

 relation which in a vertical spinal column would be called " superior," and in a hori- 

 zontal one " anterior." Similarly I use \he woTidi postaxial for what under the circum- 

 stances mentioned would be either "inferior" or "posterior." In the same way the 

 terms dorsal dca.d. ventral stand for "posterior" or "superior," and for "anterior" or 

 " inferior " respectively. 



After describing the various vertebrae throughout the spine one after another, I pro- 

 pose to describe the pelvis as a whole, then the vertebral and sternal ribs, and the sternum, 

 concluding with a recapitulation of the serial modifications the several parts and pro- 

 cesses Tmdergo as we proceed postaxially firom the atlas to the coccyx. 



There are seventeen cervical vertelree, which, in the adult, have either no rib-like 

 processes or only styliform and anchylosed ones (fig. 1, c). 



The next three vertebrae bear longer ribs, generally articulated movably with their 

 vertebrae and not directly connected with sternal ribs. They may be called cervico- 

 dorsal vertelree (fig. 1, cd). 



The next five vertebrae (twenty-first to twenty-fifth inclusive) support long ribs, which 

 unite distally with sternal ribs articulated to the sternum, and are therefore true dorsal 

 vertebra ; these vertebrae do not anchylose together or with the sacrum (fig. 1, d). There 

 are two vertebrae after these (twenty-sixth and twenty-seventh) which bear freely-ending 

 ribs or rib-like processes, and which normally anchylose with the sacrum in the adult ; 

 these can be distinguished as dorso-lumbar vertebrce. Sometimes' there may be an extra 

 ^ As in the mounted skeleton in the Bird Gallery of the British Museum. 



VOL. VIII. — PAET VII. March, 1874. 3 i 



