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Dorsal surface of sacrum

 

 
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Dorsal surface of sacrum
 
 
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The dorsal surface of sacrum is convex and narrower than the pelvic.

In the middle line it displays a crest, the middle sacral crest, surmounted by three or four tubercles, the rudimentary spinous processes of the upper three or four sacral vertebrae.

On either side of the middle sacral crest is a shallow groove, the sacral groove, which gives origin to the Multifidus, the floor of the groove being formed by the united laminae of the corresponding vertebrae.

The laminae of the fifth sacral vertebra, and sometimes those of the fourth, fail to meet behind, and thus a hiatus or deficiency occurs in the posterior wall of the sacral canal.

On the lateral aspect of the sacral groove is a linear series of tubercles produced by the fusion of the articular processes which together form the indistinct sacral articular crests.

The articular processes
Articular processes

The articular processes or zygapophyses of a vertebra, two superior and two inferior, spring from the junctions of the Pedicle of vertebral arch and Lamina of the vertebral arch....
 of the first sacral vertebra are large and oval in shape; their facets are concave from side to side, look backward and medialward, and articulate with the facets on the inferior processes of the fifth lumbar vertebra.

The tubercles which represent the inferior articular processes of the fifth sacral vertebra are prolonged downward as rounded processes, which are named the sacral cornua, and are connected to the cornua of the coccyx.

Lateral to the articular processes are the four posterior sacral foramina
Posterior sacral foramina

Lateral to the articular processes of the sacrum are the four posterior sacral foramina ; they are smaller in size and less regular in form than the anterior, and transmit the posterior divisions of the sacral nerves....
; they are smaller in size and less regular in form than the anterior, and transmit the posterior divisions of the sacral nerves
Sacral nerves

The five sacral nerves emerge from the sacrum. Although the vertebral components of the sacrum are fused into a single bone, the sacral vertebrae are still used to number the sacral nerves....
.

On the lateral side of the posterior sacral foramina
Posterior sacral foramina

Lateral to the articular processes of the sacrum are the four posterior sacral foramina ; they are smaller in size and less regular in form than the anterior, and transmit the posterior divisions of the sacral nerves....
 is a series of tubercles, which represent the transverse processes
Transverse processes

The transverse processes of a vertebra, two in number, project one at either side from the point where the Lamina of the vertebral arch joins the Pedicle of vertebral arch, between the superior and inferior articular processes....
 of the sacral vertebrae, and form the lateral crests of the sacrum.

The transverse tubercles of the first sacral vertebra are large and very distinct; they, together with the transverse tubercles of the second vertebra, give attachment to the horizontal parts of the posterior sacroiliac ligaments; those of the third vertebra give attachment to the oblique fasciculi of the posterior sacroiliac ligaments; and those of the fourth and fifth to the sacrotuberous ligaments.








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The dorsal surface of sacrum is convex and narrower than the pelvic.

In the middle line it displays a crest, the middle sacral crest, surmounted by three or four tubercles, the rudimentary spinous processes of the upper three or four sacral vertebrae.

On either side of the middle sacral crest is a shallow groove, the sacral groove, which gives origin to the Multifidus, the floor of the groove being formed by the united laminae of the corresponding vertebrae.

The laminae of the fifth sacral vertebra, and sometimes those of the fourth, fail to meet behind, and thus a hiatus or deficiency occurs in the posterior wall of the sacral canal.

On the lateral aspect of the sacral groove is a linear series of tubercles produced by the fusion of the articular processes which together form the indistinct sacral articular crests.

The articular processes
Articular processes

The articular processes or zygapophyses of a vertebra, two superior and two inferior, spring from the junctions of the Pedicle of vertebral arch and Lamina of the vertebral arch....
 of the first sacral vertebra are large and oval in shape; their facets are concave from side to side, look backward and medialward, and articulate with the facets on the inferior processes of the fifth lumbar vertebra.

The tubercles which represent the inferior articular processes of the fifth sacral vertebra are prolonged downward as rounded processes, which are named the sacral cornua, and are connected to the cornua of the coccyx.

Lateral to the articular processes are the four posterior sacral foramina
Posterior sacral foramina

Lateral to the articular processes of the sacrum are the four posterior sacral foramina ; they are smaller in size and less regular in form than the anterior, and transmit the posterior divisions of the sacral nerves....
; they are smaller in size and less regular in form than the anterior, and transmit the posterior divisions of the sacral nerves
Sacral nerves

The five sacral nerves emerge from the sacrum. Although the vertebral components of the sacrum are fused into a single bone, the sacral vertebrae are still used to number the sacral nerves....
.

On the lateral side of the posterior sacral foramina
Posterior sacral foramina

Lateral to the articular processes of the sacrum are the four posterior sacral foramina ; they are smaller in size and less regular in form than the anterior, and transmit the posterior divisions of the sacral nerves....
 is a series of tubercles, which represent the transverse processes
Transverse processes

The transverse processes of a vertebra, two in number, project one at either side from the point where the Lamina of the vertebral arch joins the Pedicle of vertebral arch, between the superior and inferior articular processes....
 of the sacral vertebrae, and form the lateral crests of the sacrum.

The transverse tubercles of the first sacral vertebra are large and very distinct; they, together with the transverse tubercles of the second vertebra, give attachment to the horizontal parts of the posterior sacroiliac ligaments; those of the third vertebra give attachment to the oblique fasciculi of the posterior sacroiliac ligaments; and those of the fourth and fifth to the sacrotuberous ligaments.

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