8S4 SKELETON 



canals for their arteries. Movable ribs are borne by one or more of 

 the lower Cervical Vertebrae, thus forming a gradual ti'ansition to 



Tlie Dorsal Vertebrae, which are composed of the same elements, 

 but are marked by the high longitudinal crest into which their 

 spinous process rises, while each of the dorsilateral processes of the 

 neural arch (which are mostly large) possesses an articular facet for 

 the tubercle of the rib, and a short ventrilateral knob near the 

 anterior end of the centrum has a similar facet for the attachment 

 of the head of the rib. Between the head and the tubercle is a 

 large foramen, the serial homologue of the/, transversarium, protecting 

 a continuation of the deep lateral strand of the Sympathetic Nervous 

 System (page 626). Dorsal vertebrae frequently exhibit a ventral 

 outgrowth of the centrum, very variable in shape and extent. 

 These outgrowths {Hypapophyses) may be simple vertical blades, or 

 JL-shaped, or paired knobs — such modifications often occurring in 

 the same bird — and they serve for the attachment of the thoracic 

 origin of the m. longus colli anticus, reaching their greatest develop- 

 ment in Sphenisci and the Colymhidse. In many birds the thoracic 

 vertebrae shew a tendency to more rigid junction, which is often 

 effected in old individuals by the ossification of the various ligaments 

 connecting the processes of adjoining vertebrae, or even by the 

 ossification of the attached tendons of the spinal muscles. In other 

 cases consolidation is carried further by the co-ossification not only 

 of the centra but also of the spinous, tranverse and zygapophysial 

 processes of adjoining vertebrae, so that in extreme cases the wiiole 

 dorsal region may become one continuous mass of bone. The 

 number of such synosteotically-connected vertebrae varies consider- 

 ably not only in closely-allied Families, genera and species, but 

 even in individuals. It is however a character that Avith care will 

 yield good taxonomic results, and thus may be depended upon as a 

 common feature in many Ciconix, Gruidx, Eallidee and Podicipedidae. 

 In most Columhse the 15th, 16th and 17th vertebrae, being gener- 

 ally the three middle thoracics, are consolidated. In Grypturi and 

 most Gallinx, in Phoenicopiterus and Pterodes the last cervical and 

 the first 3 or 4 thoracics coalesce, and in many Accipitres the first 

 4 thoracics. 



The Sacral Ver'tebrse in the widest sense are all those that are 

 overlaid by and partly fused with the iliac bones (c/. ilium, pelvis) 

 which are originally attached to not more than two of them situated 

 just behind the Acetabulum, and are the primitive or true Sacrals. 

 The iliac bones, however, during development extend considerably 

 both forwards and backwards, gradually coming into contact with a 

 variable number of others, which thus become prsesacral or post- 

 sacral vertebrae, while all those that are not reached by the anterior 

 extension of the ilia remain as Dorsals. Thus it follows that no 

 absolute line of demarcation can be drawn in regard to these 



