BIRD FROM THE WEALDEN" OF BROOK. 



207 



The bodies of the vertebrae and neural arches are both higher in 

 the anterior part of the specimen than in the posterior part, towards 

 which the depression steadily augments (fig. 3). 



Anteriorly the articular face of the first centrum is transversely 

 ovate, as among many birds, fully 15 millim. deep, and 20 millim. 

 wide, as preserved (fig. 4). It is in the main flattened, apparently 

 slightly concave from above downward, with a sharp peripheral 

 edge, now a little broken and showing fine cellular tissue. 



The posterior articular face is much smaller, and is also extended 

 transversely (fig. 5). It measures over 15 millim. wide at the base, 

 and is much narrower below the neural canal, towards which the sides 

 converge upward. It is over 9 millim. deep. There are two small 

 abraded tubercles which look downward, placed at the outer angles 

 of the base. The articular surface of the centrum is flattened, but 

 slightly concave, and has a small prominence extending backward 

 below the neural canal ; the whole surface is inclined obliquely 

 forward so as to look obliquely backward and upward. The small 

 articulation for the caudal vertebra, as compared with the inter- 

 vertebral articulation in the dorsal region, is a character which has 

 not been found in Dinosauria, and, like the transverse extension, 

 is Avian, though the latter character is also found among some 

 Ornithosaurs. The small caudal articulation implies a small tail ; 

 and it will subsequently be seen that we are entitled to infer that 

 this tail was of the type which characterizes existing birds. 



The sacrum includes six vertebrae, which are perfectly anchylosed 

 together (figs. 1, 2, 3). 



The transverse processes (figs. 1, 2, 3, t) are given oh 6 at the junction 

 of the centrums. They extend from their origin on the sides of the 

 vertebrae up to the neural platform, which is a horizontal lamina, 

 formed by the blending of the neural arches, extending along the 

 sacrum on each side of the neural spine. This platform (fig. 3, np) 

 in its anterior part is directed outward and slightly upward ; in the 

 hinder part it is horizontal. The height from the base of the 

 centrum to the neural platform at the junction of the first and 

 second vertebrae is 2*2 centim. ; at the junction of the fourth and 

 fifth vertebrae the corresponding measurement is 14 millim. The 

 neural platform does not appear to extend to the sixth vertebra. 

 The width of the neural platform at the second vertebra is 14 

 millim. ; at the fourth vertebra it is about 2 millim. wider. The 

 neural spine is broken (fig. 3, ns), but appears to form a thin con- 

 tinuous vertical plate from the second to the fifth vertebra (fig. 1, ns). 

 Its base is 3 millim. wide in front, but it is stronger in front than 

 behind. As preserved, it is only half a centimetre high in front, 

 I and its height posteriorly was less. 



The posterior aspect of the sixth neural arch is worn, so that the 

 \ zygapophyses are lost, but the neural spine is seen to be vertically 

 grooved. The first vertebra has its zygapophysial facets preserved ; 

 they have the characteristic oblique, curved, Avian position resting 

 > flat upon the neural arch (fig. 4, z). 



The sides of the centrums are compressed, and the first two show 



