ON THE VERTEBRATE SKELETON. 



327 



osseous rudiments of pleurapophyses ; and the neural spine is commonly un- 

 developed. One or more typical segments are obviously completed by the 

 meeting of the broad sides of the inverted arch (62, 63, 64) at the ' ischio- 

 pubic symphysis ' forming the ' pelvis ' of anthropotomy. Before, however, 

 entering upon the difficult inquiry into the general homology of the pelvis, 

 I would beg to refer the reader to the analysis of the sacrum of the ostrich 

 given at p. 263 : and I here subjoin a figure of seven of those vertebrae, 

 from an immature specimen, the pleurapophyses being removed from all 

 save the last (pi), in order to show the change of place of the neurapophyses 

 n 1-4, in relation to their centrums, c 1 to 4 : d d are the long diapophyses ; 

 p the short parapophyses. The sacral spines, s s, are enormously developed. 

 In the bird the modification of the vertebral segments at the posterior 



Fig. 27. 



region of the trunk in relation 

 to the transference of the whole 

 weight of the body and fore- 

 limbs (wings) upon the hind- 

 limbs, is greater and more ex- 

 tensive than in the ' bipes im- 

 plume,' and the essential nature 

 of the pelvic arch is still more 

 masked in the bird than in man. 

 In order to obtain an insight 

 into the model according to 

 which it is constructed, we must 

 descend still lower, even to the 

 humblest of the vertebrated 



Creatures that crawl upon the 7 sacral vertebrae of a young ostrich (Struthio camelus). 



earth. The example which is here selected for that purpose is the perenni- 

 branchiate amphibian called Menopome Alleghanniensis. 

 The three anterior ver- Pig. 28. 



tebrse which answer in po- 

 sition to the 'lumbar' in 

 fig. 25, differ chiefly in ha- 

 ving rudimental pleurapo- 

 physes (PI) articulated to 

 the ends of the diapophyses 

 (D)- In the next vertebra 

 the diapophysis (D') and the 

 rudimental pleurapophysis 

 (PI) are thickened and 

 enlarged: a second pleur- 

 . apophysial rib-like piece(s2) 

 is joined by one end to the 



nleuraDOohvsis and bv the Sacral vertebra and appendage with contiguous vertebrae. Menopome. 



other to a broad partially ossified cartilage (64) which meets and joins its 

 fellow, completing a haemal arch and restoring the vertebra in question to 

 the typical character. A radiated appendage, moreover, diverges on each 

 side from the articulation between 62 and 64, and forms the hind-limb. Now 

 the special homology of this limb with the undivided filamentary appendage 

 similarly situated in the lepidosiren, and with the ventral fins of fishes, in 

 the descending series ; and with the hind-limb of other reptiles, of birds and 

 of mammals in the ascending series, is unmistakeable, and, I believe, is gene- 

 rally admitted : so that comparative anatomists have not hesitated to call 

 the rib-like bone, 02, ' ilium,' and the part, 64, ' pubis * in the menopome. 



