24 ANTHROPOLOGY. 
Pl. 123, fig. 40. A dorsal vertebra from the side: *, body; *, articulating 
face for the head of a rib; °*, intervertebral notch; *, oblique process; 
*, transverse process; °, spinous process. . 
Fig. 41. A lumbar vertebra from above: ', transverse process; °, oblique 
process; *, spinous process. /vg. 42. The same from the side: ', inferior 
oblique process. 
The sacrum (figs. 48, 44) is a broad flattened triangular bone, concave 
anteriorly, convex posteriorly, inserted like a wedge between the two ossa 
innominata, and articulating with the lumbar vertebra above, with the 
coccyx below. In the young skeleton it is clearly seen to consist of five 
distinct vertebree, which become fused together or anchylosed with age, 
always, however, leaving traces of the original separation, especially on the 
anterior face. In fact, all the elements of true vertebra are here present, 
although in no high condition of development. The upper anterior pro- 
jecting edge of the sacrum is termed the promontory, behind which is the 
triangular aperture of the sacral or spinal canal. On either side of this 
canal is the oblique or articular process. The inferior extremity of the 
sacrum, or the apex, is directed downwards, sometimes a little forwards; it 
presents a small transverse, oval, convex surface, for articulation with the 
coccyx. ‘The anterior concave surface is marked by four transverse lines 
( fig. 48°), at the extremities of which on each side are four large holes (the 
antervor sacral). These transmit the anterior sacral nerves, veins, and arte- 
ries. The posterior surface is roughened by four horizontal eminences in 
the median line, corresponding with the spinous processes. On each side 
of this median ridge is a rough groove, in which are four posterior sacral 
foramina (fig. 44°), which transmit the posterior sacral nerves and some 
bloodvessels. The inferior extremity of the sacral canal is bounded poste- 
riorly by a ligament, and laterally by two tubercles, cornua sacralia, which 
descend to meet similar processes from the coccyx. 
The ossa coccygis or coccyx (pl. 122, fig. 31) correspond to the caudal 
vertebre. of animals. They consist of three or four, rarely of five pieces, 
which in the young are divisible into three parts, while in the adult 
they are united into one or two. Considering the combination into one 
piece, this in the adult is of triangular shape, serving to prolong ante- 
riorly the curve of the sacrum (fig. 5'). The base above is broad, and 
bounded by two cornua (fig. 31°), which interlock with those of. the 
sacrum. 
B. Articulations and Ligaments of the Spine. 
Articulation of the head with the spine (articulus capitis). This is a 
double arthrodia, the condyles of the occipital bone being received into the 
superior oblique processes of the atlas. The motion is quite limited, and 
restricted almost entirely to a forward and backward movement of the 
head. The capsular ligament on each side arises from the circumference of 
the condyle, and is inserted into the circumference of the glenoid cavity of 
the atlas. The interior of each capsule is lined by a synovial membrane. 
Anterior and posterior occipito-atlantal ligaments (pl. 124, fig 4°, fig. 5%”) 
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