THE ANATOMY OF BIRDS.— OSTEOLOGY. 141 
—all of them anterior to the true sacrwm of a bird. The sacrum proper (fig. 57, s) consists 
of those few vertebrae — three, four, or five — from foramina between which issue the spinal 
nerves that form the net-work called the sacral plexus. These true sacral vertebre are ribless, 
and may be recognized, in a general way, by the absence of anything like the cross-bars above 
described, issuing from the vertebral centra; though their neural arches send off some small 
bars or plates to fuse with the ilia. These sacrals proper are at or near the middle of the 
whole sacral mass. After these come a large number — from five to ten or more — of verte- 
bree which, from their following the true sacrals, though consolidated therewith and with one 
another, are considered to belong to what would be the caudal region of other animals, and 
are hence ealled ‘‘ tail-sacrals,” wro-sacrals (Gr. ovpa, tail, fig. 57, c.) These continue to send 
off a series of little plate-like processes from their neural arches, just as the true saecrals do; 
but, in addition to these, processes are given off from the bodies of the uro-sacrals, corre- 
sponding in position and relation to those which proceed from the bodies of the lumbars, and 
being apparently of the same morphological character (pleurapophysial). These ‘“ riblets ” 
are, however, quite slender, and also oblique in two directions; for instead of being trans- 
verse and nearly horizontal, they trend very obliquely backward and upward; they also 
shorten consecutively from before backward. The cross-bars of the latter uro-sacrals, however, 
are stouter and altogether more like those of a lumbar vertebra. The appearances described 
are those seen from below, or on the ventral aspect. Above, on the back of the pelvis, the 
line of confluent spinous processes of the dorso-lumbars is commonly distinct, separated a little 
from the flaring lips of the ilia. Such distinct formation may continue throughout the sacral 
and uro-sacral regions; oftener, however, the line of spimous process sinks, flattens, and 
widens into a horizontal plate which becomes perfectly confluent with the ilia along the pos- 
terior 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 inter- 
vertebral foramina. — Such is the general character of a bird’s complex sacrum; the description 
is taken chiefly from a raven (Corvus corax) ; the figure from the common fowl, after Parker. 
The kidneys are moulded into the recesses between the sacral and uro-sacral vertebra and in 
the concavity of the ilia. The general shape of a ‘‘ sacrum,” viewed from below, is fusiform, 
broadest across the sacral bodies proper or just in front of them, tapering toward either end; 
the face of the sacrum is also flattest about the middle, more or less ridged before and behind 
froin compression of the vertebral bodies. It has little if any lengthwise curvature, and that 
chiefly in the uro-sacral region, where the concavity is downward. The total number of bones 
may be less than twelve, or more than twenty. The extensive anchyloses in this region of 
the spme are in evident adaptation to bipedal locomotion, which requires fixity hereabouts, 
that the trunk may not bend upon the fulerum 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 word ‘‘ sacrum,” a ‘‘ sacred thing,” curious in this application, is very 
ancient in human anatomy, commemorating some superstitious or ritualistic notion, respecting 
this part of the body.) 
The Coccygeal, or Caudal Vertebre (fig. 56, clv) proper, terminate the spinal column. 
They are called ‘‘ coceygeal,” from the fancied resemblance of the human tail-bones collectively 
to the beak of a cuckoo (Gr. kéxkv&, kokkux). The caudals are all the free bones situated 
behind the anchylosed uro-sacrals. 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 Archeopteryx 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 diminish the spimal cord that a mere thread is left to pene- 
