PEOPESSOE OWEN ON THE GENUS DINORNIS. 177 



caudal series of vertebrae, of which five have been enlisted or conscripted into the 

 service of the sacrum. 



The sacro-neural canal (Plate XXXI. fig. 2) retains a vertical diameter of 8 lines 

 along the first three vertebrae ; it then expands gradually to the sixth and rapidly to 

 the ninth sacral, where the vertical diameter reaches to 1 inch 6 lines. The anterior or 

 'haemal' myelonal columns would seem to have made a bulge between the eighth 

 and tenth vertebrae ; and the neural canal, again contracting, shows its diameter of 

 8 lines between the thirteenth and fourteenth outlets, and is reduced to 4 lines in 

 the last or seventeenth sacral vertebra. 



The motory and sensory divisions of the nerve-outlets continue distinct to the outer 

 surface of the vertebra as far as the twelfth, the neural (dorsal, upper) or sensory 

 division being the smallest, and diminishing more rapidly than the haemal (lower, 

 motory) outlet after the ninth of these. The canal gains in transverse as in vertical 

 expanse, but in a rather less degree. 



Parapophysial abutments cease after the eighth sacral, and are resumed at the 

 twelfth. The diapophysial ones increase in length from the fifth sacral, but with 

 much diminished breadth, to the ninth sacral, when they increase in breadth as well 

 as length, and curve upward, backward, and slightly outward to buttress up the 

 expanded postacetabular part of the ilium. 



Between the smooth compact inner layer of bone forming the neural canal and the 

 somewhat thicker outer layer, the osseous substance of the sacrum is coarsely reticulate 

 and pneumatic. Larger subserial vacuities mark, in vertical section (Plate XXXI. 

 fig. 2), some of the anterior obliterated vertebral interspaces ; and the longest or chief 

 laminae, rising from the roof of the neural canal, indicate the neural spines at distances 

 corresponding to the nerve-outlets, answering to the fourth sacral vertebra. The 

 spine-plate curves gently forward ; while those of the sixth, seventh, and eighth sacrals 

 rise vertically, and the succeeding ones curve gently backward. 



In the comparison of the sacrum of Binornis, as exemplified by the present spines, 

 with that of Strufhio, as illustrated in Prof Mivart's paper i, I may premise that the 

 first three (anchylosed) vertebrae are reckoned, by its author, as ' dorso-lumbar ' (26th 

 and 27th) and lumbar (28th) vertebrae. It will be understood, therefore, that in my 

 description of the specimen " in the Museum of the College of Surgeons" ^, figured 

 in Mivart's cut 59, " the neural arch of the fifth sacral vertebra has advanced, 

 and rests over the interspace between its own and the preceding centrum; at the 

 eleventh vertebra it has resumed its normal position and connexions." My ' fifth sacral ' 

 is Mivart's ' second ' (s 2), and my ' eleventh ' sacral is Mivart's eighth ; the last five 

 sacrals in the twenty anchylosed vertebrae of the mature Ostrich ^ are reckoned by him 

 as the first five caudals in that bird. 



' Loc. cit. pp. 420^27, figs. 58-62. = ' Catalogue ' ut supra, 4to, 1853, p. 266. 



' Trans. Zool. Soo. vol. iii. pi. 19. fig. 4. 



