176 PEOFESSOE OWEN ON THE GENUS DINOENIS. 



Dinosaurian vertebrae figured in plates xii. et seq. of my ' History of British Fossil 

 Reptiles '1. Every subsequent discovery of a true Dinosaur has confirmed the appli- 

 cability and value of this character of the extinct order. 



The sacrum in Dinorms I continue to characterize, as in other birds, by the anchy- 

 losis of the vertebrae, through which that single mass of the ' spinal column ' results. 

 The concomitant anchylosis of the iliac, ischial, and pubic bones constitutes the 

 ' pelvis.' In birds " anchylosis converts a large proportion of the vertebral column into 

 a sacrum"^. When it is said, and legitimately in its taxonomic application, that " the 

 Cetacea have no sacrum," it is to be understood that vertebrae homologous with the 

 sacrals of the bird have not coalesced : when a mammal is said to have but two " sacral 

 vertebrae," the homologues of two of the sacral vertebrae of the bird have coalesced. In 

 Dinornis maximus seventeen vertebrae have so coalesced, and include the homologues 

 of vertebrae which in mammals retain their primitive freedom, and may be characterized 

 as ' dorsal,' ' lumbar,' and ' caudal.' When it is said that birds have no lumbar vertebrae, 

 a similar remark applies to that which has been offered respecting the absence of sacral 

 vertebrae in the Cetacea. 



The first or foremost sacral vertebra in Dinornis maximus (twenty-third of the entire 

 series) offers to its pleurapophysis, which retains its mobility, a parapophysial cup near 

 the upper and fore part of the centrum, and a small rough facet on its diapophysis. 

 The pleurapophyses of the second and third sacrals are anchylosed each to its parapo- 

 physis, and thence, by a bony plate, continued from the upper part of the ' cervix ' to 

 the lower part of the diapophysis. These two last ribs are progressively shortened, 

 but still project beyond the iliac roof. Their more reduced serial homologues form 

 the transverse osseous bars abutting against the outswelling antacetabular part of the 

 ilium, with which the pubis has coalesced (Trans. Zool. Soc. vol. iii. pi. xix. fig. 2). 



After the second sacral centrum that element, in succeeding vertebrae, quickly loses 

 length. In the section of the sacrum of Dinornis maximus (PI. XXXI. fig. 2, f nat. size) 

 the interval between the first (] ) and second nerve-outlets, which is 2 inches 7 lines, is 

 reduced to 6 lines between the sixth (e) and seventh outlets, and to a less extent in the 

 four succeeding outlets. Between the twelfth (12) and thirteenth outlets the interval 

 is 9 lines, and it increases to 1 inch 6 lines between the fifteenth and sixteenth (lu) 

 outlets. Of these nerve-outlets, the separation of the motory from the sensory division 

 is well marked at their commencement from the neural canal in the fourth sacral, and 

 so continues to the twelfth. In the thirteenth the size of the outlet is much reduced : 

 from this part the myelon is restricted to the supply of the terminal contracted part of 

 the spinal column called ' tail ; ' and here we have the sign of the beginning of the 



' Quarto, part vi. (1855). 



- ' Anat. of Vertebrates,' 8vo, 1866, ii. p. 29. The homologies of certain of these with the vertebrEe called 

 ' dorsal,' ' lumbar," and ' caudal,' in other vertebrate classes, are given in my ' Archetype,' &c., 8vo, 1848, 

 p. 90 et seq. 



