232 THE ARTICULATIONS 



one set of processes over the sharp upper edges of the other, which would be necessary for 

 forward flexion. A fair amount of lateral inclination would be permitted but for the impedi- 

 ment offered by the ribs; while the position and direction of the articular processes allows rota- 

 tion round a vertical axis which passes through the centres of the bodies of the vertebrae. This 

 rotation is not very great, and is freer in the upper than in the lower part of the thoracic 

 region. 



In the lumbar region, extension and flexion are very free, especially between the third and 

 /fourth and fourth and fifth vertebrae, where the lumbar curve is sharpest; lateral inclination 

 { is also very free between these same vertebrae. It has been stated that the shape and position 

 i of the articular processes of the lumbar and the lower two or three dorsal are such as to prevent 

 I any rotation in these regions; but, owing to the fact that the inferior articular processes are not 

 / tightly embraced by the superior, so that the two sets of articular processes are not in contact 

 .^ on both sides of the bodies at the same time, there is always some space in which horizontal 

 motion can occur round an axis drawn through the central part of the bodies and interverte- 

 bral discs, but it is very slight. Thus, the motions are most free in those regions of the column 

 which have a convex cm-ve forward, due to the shape of the intervertebral discs, where there 

 are no bony walls surrounding solid viscera, where the spinal canal is largest and its contents 

 are less firmly attached, and where the pedicles and articular processes are more nearly on a 

 transverse level with the posterior surface of the bodies of the vertebrae. 



Nor must the uses of the ligamenta flava be forgotten: these useful structures — (1) com- 

 plete the roofing-in of the vertebral canal, and yet at the same time permit an ever-changing 

 variation in the width of the interlaminar spaces in flexion and extension; (2) they also restore 

 the articulating surfaces to their normal position with regard to each other after movements 

 of the column; (3) and by forming the medial portion of each articular capsule, they take the 

 place of muscle in preventing it from being nipped between the articular surfaces during 

 movement. ^ 



Muscles which take part in the movements of the vertebral column. — Flexors : When acting 

 /with their fellows of the opposite side. Rectus abdominis, infra-hyoid muscles (slightly) 

 sterno-mastoid, external obhque, internal obUque, intercostals, scalenus anterior, psoas 

 major and minor, longus colli, longus capitis (rectus capitis anterior major). 



Extensors : When acting with their feUows of the opposite side. Sacro-spinalis, quadratus 

 lumborum, semispinalis, multifidus, rotatores, interspinales, serrati posteriores, the splenius, 

 and with the scapula fixed the levator scapulae and the upper fibres of the trapezius. 



Muscles which help to incline the column to their own side. — Sacro-spinalis, quadratus 

 lumborum, semispinalis, multifidus, the intercostals helping to fix the ribs, the external and 

 internal oblique muscles, levatores costarum, serrati posteriores, the scalenes, splenius cervicis, 

 longus colU (oblique part), rotatores, inter transversales, psoas, and with the scapula fixed the 

 levator scapuhe and the upper and lower fibres of the trapezius. 



Muscles which rotate the column and turn the body to their own side. — Splenius cervicis, 

 internal oblique (the ribs being fixed), serratus posterior inferior, and with the scapula fixed 

 the lower fibres of the trapezius. 



Muscles which rotate the column and turn the body to the opposite side. — Multifidus, 

 semispinalis, external oblique, the lower oblique fibres of the longus colli, and with the scapula 

 md humerus fixed the latissimus dorsi and trapezius. ^ 



2. THE SACRO-VERTEBRAL ARTICULATIONS 



(a) Class. — False Synchondrosis. 



(6) Class. — Diarthrosis. Subdivision. — Arthrodia. 



As in the intervertebral articulations, so in the union of the first portion of the 

 sacrum with the last lumbar vertebra, there are two sets of joints — viz. (a) a 

 synchondrosis, between the bodies and intervertebral disc; and (6) a pair of 

 arthrodial joints, between the articular processes. The union is effected by the 

 following ligaments, which are common to the vertebral column: — (i) anterior, 

 and (iij posterior longitudinal; (iii) lateral or short vertebral; (iv) capsular; (v) 

 ligamenta flava; (vi) supraspinous and (vii) interspinous ligaments. Two 

 special accessory ligaments on either side, viz., the sacro-lumbar and the ilio- 

 lumbar, connect tlie pelvis with the fourth and fifth lumbar vertebra). 



The sacro-lumbar ligament (fig. 271) is strong, and triangular in shape. Its 

 apex is above and iiK^dial, being attached to tKc whole of the lower border and 

 front surface of the transverse process of the fifth lumbar vertebra, as well as to 

 the pedicle and body. It is intimately blended with the ilio-luiuhar ligament. 

 Below, it has a wide, fan-shaped attachment, extending from the edge of the ilio- 

 lumbar ligament forward to the brim of the true pelvis; blending with the perios- 

 teum on the base of the sacrum and in tlie iliac fossa, and with the superior sacro- 

 iliac ligament. 



By its sharp medial l)()rdf'r it liinits laterally the foramen for the lasl lumbar nerve. It is 

 pierced by two large foramina, which transmit arteries to the sacro-iliao synchondrosis. This 

 ligament is in series with the iiitcrtninsvnrso ligaments of the spinal column. It is sometimes 

 described as a part of the ilio-lumbar ligament. 



