Base of the sacrum
Encyclopedia
The base of the sacrum, which is broad and expanded, is directed upward and forward.
In the middle is a large oval articular surface, the upper surface of the body of the first sacral vertebra, which is connected with the under surface of the body of the last lumbar vertebra by an intervertebral fibrocartilage
.
Behind this is the large triangular orifice of the sacral canal
, which is completed by the laminae
and spinous process
of the first sacral vertebra.
The superior articular processes project from it on either side; they are oval, concave, directed backward and medialward, like the superior articular processes of a lumbar vertebra.
They are attached to the body of the first sacral vertebra and to the alae by short thick pedicles; on the upper surface of each pedicle is a vertebral notch, which forms the lower part of the foramen between the last lumbar and first sacral vertebrae.
On either side of the body is the ala of sacrum
.
In the middle is a large oval articular surface, the upper surface of the body of the first sacral vertebra, which is connected with the under surface of the body of the last lumbar vertebra by an intervertebral fibrocartilage
Fibrocartilage
White fibrocartilage consists of a mixture of white fibrous tissue and cartilaginous tissue in various proportions. It owes its flexibility and toughness to the former of these constituents, and its elasticity to the latter...
.
Behind this is the large triangular orifice of the sacral canal
Sacral canal
The vertebral canal runs throughout the greater part of the sacral bone; above, it is triangular in form; below, its posterior wall is incomplete, from the non-development of the laminæ and spinous processes....
, which is completed by the laminae
Lamina of the vertebral arch
The laminæ are two broad plates, extending dorsally and medially from the pedicles, fusing to complete the roof of the vertebral arch.Their upper borders and the lower parts of their anterior surfaces are rough for the attachment of the ligamenta flava....
and spinous process
Spinous process
The spinous process of a vertebra is directed backward and downward from the junction of the laminae , and serves for the attachment of muscles and ligaments. In animals without an erect stance, the process points upward and may slant forward or backward...
of the first sacral vertebra.
The superior articular processes project from it on either side; they are oval, concave, directed backward and medialward, like the superior articular processes of a lumbar vertebra.
They are attached to the body of the first sacral vertebra and to the alae by short thick pedicles; on the upper surface of each pedicle is a vertebral notch, which forms the lower part of the foramen between the last lumbar and first sacral vertebrae.
On either side of the body is the ala of sacrum
Ala of sacrum
On either side of the body of the base of the sacrum is a large triangular surface, which supports the Psoas major and the lumbosacral trunk, and in the articulated pelvis is continuous with the iliac fossa...
.