MOVEMENTS OF THE VERTEBRAL COLUMN 175 



spinous bursa occurs usually over the fourth thoracic spine, but may be over the 

 third and may extend to the fifth.'' In the neck the funicular part consists for the 

 greater part of two bands closely applied and attached to each other. Near and at 

 the withers it broadens greatly, forming an expansion three to five inches (ca. 8 to 

 12.5 cm.) in width, the lateral margins of which are thin and overlie the trapezius 

 and rhomboideus muscles. Behind the higher spines it becomes narrower and 

 thinner, and is continued by the white fibrous lumbo-dorsal ligament." A mass 

 of fat and elastic tissue lies upon the ligament as far back as the withers. It 

 varies greatly in amount in different subjects, and is most developed in stallions of 

 draft breeds, in which it forms the basis of the " crest." The lamellar portion (Pars 

 cervicalis) consists of two laminse separated medially by a layer of loose connective 

 tissue. Each lamina is formed of digitations which arise from the second and third 

 thoracic spines and from the funicular portion, are directed downward and forward, 

 and end on the spines of the cervical vertebra^, except the first and last. The digita- 

 tion which is attached to the spine of the axis is very thick and strong. Behind 

 this they diminish in size and strength; that to the sixth cervical is quite thin and 

 feeble, or may be absent. 



The interspinous ligaments (Ligamentainterspinalia)extend between the spines 

 of contiguous vertebrae. In the cervical region they are narroAV elastic bands, and 

 in the thoracic and lumbar regions they consist of white fibers directed obliquely 

 downward and forward. 



The intertransverse ligaments (Ligamenta intertransversaria) are membranes 

 which connect adjacent transverse processes in the lumbar region. 



INTERTRANSVERSE ARTICULATIONS 

 These joints (peculiar to equidae) are diarthroses formed by the transverse 

 processes of the last two lumbar vertel)ra? and the alae of the sacrum. A similar 

 joint between the fourth and fifth lumbar processes is frequently present. The 

 articular surfaces have an elongated oval form, the anterior one being concave and 

 the posterior one convex. The capsule is tight, and is reinforced ventrally. 



SACRAL AND COCCYGEAL ARTICULATIONS 



In the foal the bodies of the five sacral vertebrae form joints which resemble 

 somewhat those in the posterior part of the lumbar region. These joints are in- 

 vaded by the process of ossification early, so that the consolidation of the sacrum 

 is usually complete, or nearly so, at three years. 



The coccygeal vertebrae are united by relatively thick intervertebral fibro- 

 cartilages, which have the form of biconcave discs. Special ligaments are not 

 present, but there is a continuous sheath of fibrous tissue. The movement in this 

 region is extensive and varied. In old horses the first coccygeal vertebra is often 

 fused with the sacrum. 



MOVEMENTS OF THE VERTEBRAL COLUMN 



The movements of the spine, exclusive of those at the atlanto-axial joint, are 

 dorsal, ventral, and lateral flexion, and rotation. The range of movement at a 

 single joint is very small, but the sum of the movements is considerable. The 



' In dissecting-room subjects these bursse and the adjacent structures are commonly the seat 

 of pathological changes. They appear to be the starting-point of "poll evil" and "fistulous 

 withers." 



^ No natural line of demarcation exists between the ligamentum nuchs and the lumbo-dorsal 

 continuation of the supraspinous ligament, since the change from tlie purely elastic to the white 

 fibrous structure is gradual. 



