SEC. IV ANATOMY OF BIRDS 209 



the ventral aspect. Above, on the back of the pelvis, the line of 

 confluent spinous processes of the dorsolumbars is commonly dis- 

 tinct, separated a little from the flaring lips of the ilia. Such dis- 

 tinct formation may continue throughout the sacral and urosacral 

 regions ; oftener, however, the line of spinous process sinks, flattens, 

 and widens into a horizontal plate which becomes perfectly con- 

 fluent with the ilia along the posterior portion of their extent ; such 

 smooth, somewhat lozenge-shaped surface being quite continuous 

 with the superficies of the pelvis, but perforated with more or fewer 

 pairs of intervertebral foramina. — Such is the general character of a 

 bird's complex sacrarium, as I name the whole mass of bones that are 

 ankylosed together, including dorsolumbars and urosacrals, as well 

 as sacrum proper. The description is taken chiefly from a raven 

 (Gorims corax) ; the figure from the common fowl, after Parker. 

 The kidneys are moulded into the recesses between the sacral and 

 urosacral vertebrae and in the concavity of the ilia. The general 

 shape of a sacrarium, viewed from below, is fusiform, broadest 

 across the sacral bodies proper or just in front of them, tapering to- 

 ward either end ; the face of the sacrarium is also flattest about the 

 middle, more or less ridged before and behind from compression of 

 the vertebral bodies. It has little if any lengthwise curvature, and 

 that chiefly in the urosacral region, where the concavity is down- 

 ward. The total number of bones may be less than twelve, or more 

 than twenty. The extensive ankyloses in this region of the spine 

 are in evident adaptation to bipedal locomotion, which requires 

 fixity hereabouts, ^that the trunk may not bend upon the fulcrum 

 represented by a line drawn through the hip-joints, which are 

 situated about opposite the middle of the sacral mass, as shown by 

 the arrow, ac, in Fig. 60. 



The Coecygeal, or Caudal Vertebrae (Fig. 56, ch) proper, ter- 

 minate the spinal column. They are called " coccygeal," from the 

 fancied resemblance of the human tail-bones collectively to the beak 

 of a cuckoo (Gr. kokkv^, hohhux). The caudals are all the free bones 

 situated behind the ankylosed urosacrals. The series commonly 

 begins opposite the point where the pelvic bones end ; it consists of 

 a variable number of bones, from the twenty long slender ones 

 which the Archcevpteryx possessed, down to seven or fewer separate 

 ones. The usual number is eight without the pygostyle. They are 

 stunted, degraded vertebrae, whose chief office is to support the tail- 

 feathers : for the leash of nerves which emerge from the spinal 

 canal to form the sacral plexus by so much diminishes the spinal 

 cord that a mere thread is left to penetrate the tail, though the 

 neural arches of all the coccygeals be still pervious. All may be 

 freely movable, as in the American Ostrich (Ehea) ; but in almost 

 all birds only the anterior ones are distinct and vertebra-like, the 



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