213 

 1 104. Two cervical vertebra; of a young Ostrich (Sfrttttio Camd**). 



They ihow the plcurapophyses, or rudimental vertebral ribs, mill uiuuichyloscd to the par 

 apophysi* below and the diapophysis above. The neural arch coalesce* very early with tin 

 centrum in all birds. The anterior articular surface of the centrum is convex vertically, con- 

 cave transversely, and the reverie on the posterior surface ; so that they are joined by slightly 

 iiitrrlocking trochlear articulationi. The anterior sygapophy*e look obliquely upwards and 

 inward*, and the posterior one* downwards and outward*: the neural canal is slightly ex- 

 panded at it* outlet*. 



Pretexted by Prof. Owen, F.R.S 



\ 105. A dorsal vertebra, in longitudinal section, of an Ostrich (Strut kio Cameltu). 



It shows the loose cancellou* texture, and the orifices by which the air is admitted therein. 

 The pleurapophyse* have been removed ; they do not become anchylosed, as in the neck, but 

 leave articular surfaces upon the centrum and diapophysi*. 



Htmteria*. 



1106. The vertebrae of the trunk of a Pelican (PeJecaiuu Onocrotaliu), from tin 

 middle of which a segment has been removed by vertical section. 



The cut surface* show the light cellulosity of the centrum, neural arch and sternum. The 

 following letters indicate the elements of the modified vertebra; of the thorax : r. centrum . 

 p. parapophysi* ; d. diapophysi* ; it. neural arch and rudimental spine ; pi. pleurapophysis . 

 A. hcmapophysis ; A. . haemal spine. The tendency of individual elements and bones Ui 

 coalesce in birds has already been illustrated in the cranium ; it is here shown not only by 

 the confluence of the centrum with the neural arch, but by that of several consecutive cen- 

 trums and arches into a single bone. In like manner the hsemal spines, which continue 

 distinct in many Vertebral*, have here coalesced into a single bone, which articulates on each 

 side with the luemapophyses of several vertebrae. These coalesced spines are also much de- 

 veloped in breadth, and send down from the middle of their under surface a longitudinal 

 crest or keel. This modification relates to the extension of the surface for the origin of the 

 great muscle* of flight, and renders the ' sternum,' a* the coalesced series of spines is called. 

 one of the moat characteristic parts of the skeleton of the bird. Ossification extends from 

 the neural arches into the tendon* of the vertebral muscles, and such bone-tendons, both 

 here and in other part* of the body, a* the leg*, are also characteristic of birds. The sca- 

 pula is long and slender, a* in the Ckelonta ; but is usually more compressed and sabre - 

 shaped than in the Pelican. The coracoid, a* a general rule, is a distinct bone, moveably 

 articulated to the scapula at one end and to the sternum at the other. Its broad sternal eml 

 here articulate* by a kind of gomphosis with a deep groove on the fore part of the sternum. 

 The clavicle articulate* with the coracoid above, but is confluent with it* fellow and with the 

 keel of the sternum below. The iliac bone* are remarkable for their length, and for tin- 

 number of the vertebrae, or the great extent of the confluent spinal column, to which they 

 are anchylosed ; they reach in the present instance, and in most other birds, from the tail 

 forwards to the vertebra: with moveable rib* : thus the artificial characters of a 



