OSSEOUS SYSTEM OF AVES. 31 



increase in length and thickness. The breadth of these vertebra? 

 also gradually increases ; but it diminishes in the four succeeding 

 vertebra?, in which the parapophyses are wanting : then the ninth 

 and tenth sacral vertebra? send outward each a pair of strong 

 parapophyses to abut against the inner surface of the ossa inno- 

 niinata immediately behind the acetabulum : the anchylosis of the 

 bodies is continued through the four succeeding vertebras, which 

 are of a very simple structure, devoid of transverse or oblique 

 processes, becoming gradually more compressed and more extended 

 vertically, so as to appear like mere bony lamina? ; the line of the 

 articulation between the bodies of these posterior sacral vertebra? 

 is obvious, but their spines coalesce to form a continuous bony 

 ridge, which is closely embraced by the posterior extremities of 

 the ilia. The foramina for the nerves are pierced in the sides of 

 the bodies of the sacral vertebrte ; they are double in the anterior 

 ones, but single in the posterior compressed vertebra?, where they 

 are seen close to the posterior margin. 



The species of Dinornis show from 17 to 20 sacral vertebni?. 

 In D. rohustus the pleurapophyses of the first retain their move- 

 able articulations : those of the second and third are anchylosed, 

 but project freely beyond the ilia : those of the fourth to the 

 eighth abut as parapophyses against the ilia, the last, which is oppo- 

 site the acetabula, being the thickest : those and the four following 

 sacrals, which have no parapophyses, are very short : from the thir- 

 teenth to the twentieth sacral the parapophysial buttresses reap- 

 pear, and the vertebra? increase in length. A continuous bony 

 roof of the pelvis extends from the sacral spines to the ilia. When 

 vertically and longitudinally bisected, the sacrum shows the great 

 expanse of the canal for that part of the myelon in connection with 

 the nerves of the large and strong hinder extremities. All traces 

 of the original joints between the bodies of the vertebras, wdth the 

 exception of the last, are obliterated. The primitive distinction 

 of the neural arches is indicated by undulating transverse folds of 

 the roof of the spinal canal : the motor and sensitive roots issue 

 separately, as in other birds. 



In the Penguins (yAiJtenodytes) the sacrum forms the middle 

 third of the upper surface of the pelvis : in Podiccps and Colymhus 

 the ilia converge to the summits of the posterior sacral spines : in 

 Uria, Diomedea, Procellaria, and the AnatidcB they converge to 

 the anterior ones, fig. 22, b. Pairs of foramina usually indicate the 

 sacral vertebrae, forming a broader posterior sacral roof (ib. a, c), 

 of the pelvis : but in the Petrels ossification obliterates them. In 

 most Grallatores the ilia come near to the neurospinal ridge, ib. />», 



