60 



SPECIAL ANATOMY OF THE SKELETON 



developed, and correspond in shape and direction to the superior articulating 

 processes of a lumbar vertebra; the second and third are small; the fourth and fifth 

 (usually blended together) are situated on each side of the sacral canal and assist 

 in forming the sacral cornua. External to the articular processes are the four 

 posterior sacral foramina (foramina sacralia posteriora); they are smaller in size 

 and less regular in form than the anterior, and transmit the posterior branches 

 of the sacral nerves. On the outer side of the posterior sacral foramina is a series 

 of tubercles, the rudimentary transverse processes of the sacral vertebrae (cristae 

 sacrales laterales). The first pair of transverse tubercles are large, very distinct, 

 and correspond with each superior angle of the bone; they together with the 



Erector spinse. 



Latissimus dorsi. 



Erector spinse. 



Upper half of ffth 

 posterior sacral foramen. 



FIG. 25. Sacrum, dorsolateral view. 



second pair, which are of small size, give attachment to the horizontal part of 

 the sacroiliac ligament; the third gives attachment to the oblique fasciculi of 

 the posterior sacroiliac ligaments; and the fourth and fifth to the great sacro- 

 sciatic ligaments. The interspace between the spinous and transverse processes 

 on the back of the sacrum presents a wide, shallow concavity, called the sacral 

 groove; it is continuous above with the vertebral groove, and lodges the origin 

 of the Multifidus spinae. 



Lateral Surface. The lateral surface, broad above, becomes narrowed into a 

 thin edge below. Its upper half presents in front a broad, ear-shaped surface for 

 articulation with the ilium. This is called the auricular surface (fades auricularis), 

 and in the fresh state is coated with fibrocartilage. It is bounded posteriorly 

 by deep and uneven impressions, for the attachment of the posterior sacroiliac 

 ligaments. The chief prominence is called the tuberosity (tuberositas sacralis]. 

 The lower half is thin and sharp, and terminates in a projection called the inferior 



