OSSEOUS SYSTEM OF AVES. 17 



1-4, the anchylosis extends from the second to the fifth dorsal ver- 

 tebra. In the Sparrow-hawk, tlie same vertebra3 are consolidated 

 into one piece, while the sixth enjoys considerable lateral motion, 

 both upon the fifth and seventh, which last is anchylosed to the 

 sacrum ; so that the body can be rapidly and extensively inflected 

 toward either side during the pursuit of prey. 



From some or most of the dorsal centrums inferior processes 

 (hypapophyses) are sent down, for extensive and favourable origin 

 of the flexor muscles, longi colli and recti antici, of the neck. In a 

 vulture {Gi/ps fulvus) the hypapophysis is a low median ridge in 

 the first and second dorsals ; to this, in the third dorsal, is added 

 a pair of outstanding depressed plates : in the fourth the pair of 

 plates are smaller, and, mth the medial ridge, are supported on a 

 common stem: in the fifth dorsal, the hypapophysis is again 

 reduced to a median compressed plate, but it is expanded at the 

 end ; the vertebra, which by anchylosis has become the foremost 

 sacral, has a similar but stronger and slightly bifurcate hypapophy- 

 sis. In both Vultures and Eagles the parial hypapophyses are seen 

 to be due to modified parapophyses, which descend and are pro- 

 gressively lost in the median hypapophysis of the fourth and fifth 

 dorsals {^Harpcya, Cuv.) ; the sixth and seventh liave only tlie 

 low median ridge. The parapophysial pairs of inferior processes 

 are broad divergent plates in the anterior dorsals oi Aptenoclyfcs^ 

 and Alca^, and subside upon the large and long compressed median 

 hypapophysis wdiich characterises the posterior dorsals. Tlie 

 unusual developement of these inferior processes relates to the size 

 and strength of the subvertebral muscles, which combine w^th 

 other muscles of the trunk in the shuffling movement by which 

 the Penguin, like the seal, makes progress, prone, upon dry Land, 

 In the anterior dorsals the parapophysis, besides forming the arti- 

 culation for the head of the rib, sends ofi" a muscular process sub- 

 ject to the modifications above mentioned: the diapophysis is 

 larger and more constant in character ; it is extended from before 

 backward, is horizontally flattened, and forms the surface for the 

 joint of the tubercle of the rib at a small part of its outer border : 

 a metapophysial ridge is developed from the upper surface, and is 

 frequently produced into filaments coalescing with those of conti- 

 guous dorsals. The pneumatic foramina are at the back part of 

 the base of the diapophyses. The zygapophyses are small, the front 

 pair look upward and inward; the back pair outward and downward ; 

 the latter often support anapophysial ridges. The neural spine is a 



' X-. pi. 51, fig. 48, h, h. 2 XH-. 



VOL. II. C 



