OSSEOUS SYSTEM OF AVES. 



15 



First tlirce dorsal vertebnv and scapular 

 arch of a bird, in diagrammatic side view. 



Ill fig. 12, is given a sketch of three dorsal segments, i, 2, 3, 

 with the hiemal arches, 52, 58, of 

 two others. In the first and se- 

 cond dorsals the pleurapophyses (i 

 and 2) terminate in a free pointed 

 end, like the ' false floating ribs,' of 

 Anthropotomy ; in the third, the 

 plenrapophysis, pi, .s, articulates 

 with the haiinapophysis, h ; and this 

 Avith the expanded spine, h s, which, 

 in connation with its homotypes, 

 constitutes the bone called ' ster- 

 num,'/*. Every succeeding dorsal 

 segment has the ha3mal arch com- 

 pleted by bone. 



Fig. 13, gives a diagrammatic front view of the connate dorsal 

 or thoracic ha3mal spines, c, s; the ha^mapophyses, d, of five 

 corresponding segments, and also a modified pair, A, h, of the ha3m- 

 apophyses of an antecedent segment. 



The pleurapophyses, pZ, «, 

 of the dorsal segment are 

 shown in connection with the 

 centrum, c, and neural arch, 

 71 ; it is to this part of the 

 segment that the term ' verte- 

 bra,' is commonly restricted. 



The dorsal vertebra?, thus 

 defined, rarely form more than 

 a fourth part of the entire 

 column, and in some of the 

 long-necked Grallatores, as 

 the Stork and Flamingo, fig. 

 14, form only an eighth part ; 

 they have not been observed 

 to be fewer than four (in some 

 Vultures), nor more than nine 

 throughout the class ; the lat- 

 ter number obtains in the Ap- 

 teryx : the most common numbers are six or seven. 



The dorsal vertebra? are shorter than most of the cervicals, and 

 Avith broader neural arches, in consequence of the greater devc- 

 lopcinent of the transverse processes ; but their bodies become mucli 

 compressed, and in some Birds are reduced almost to the form of 



1 tenor vertebra, witii other iKvmal arches of dorsal 

 or thoracic region, in diagrammatic front view. 



