SACBAL AND COCCYGEAL ARTICULATIONS 213 



and withers it is remarkably modified to form the ligamentum nucha which re- 

 quires more extended notice. 



The Ugamentum nuchas is a powerful elastic apparatus, the principal function 

 ot which IS to assist the extensor muscles of the head and neck. It extends from 

 the occipital bone to the withers, where it is directly continuous ^\dth the lumbo- 

 dorsa part of the supraspinous ligament. It consists of two parts— funicular and 

 lamellar. The funicular part (Pars occipitalis) arises from the external occipital 

 protuberance and is inserted into the summits of the vertebral spines at the withers 

 iwo bursas are usually found under it in the adult. The atlantal bursa lies be- 

 tween the hgament and the dorsal arch of the atlas. The supraspinous bursa is 

 usually over the third and fourth thoracic spines, but may be over the second or 

 extend to the fifth.^ Another bursa may be present at the spine of the axis; this is 

 between the funicular part and the large digitation attached to the axis. 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 ex- 

 pansion about five to six inches (ca. 12 to 15 cm.) in width, the lateral margins of which 

 are thin and turn do^vn over the trapezius and rhomboideus muscles. Behind the 

 higher spines it becomes narrower and thinner, and is continued by the white fibrous 

 lumbo-dorsal part.^ 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 stalhons of draft breeds, in which it forms the basis of the so-called 

 "crest." The lamellar part (Pars cervicalis) consists of two laminaj 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 part, 

 are directed downward and forward, and end on the spines of the cervical vertebra, 

 except the first and last. The digitation which is attached to the spine of the axis 

 is very thick and strong. Behind this they diminish in size and strength; the last 

 one, which is attached to the sixth cervical vertebra, is quite thin and feeble, or may 

 be absent. 



The interspinous ligaments (Ligg. interspinalia) extend between the spines 

 of contiguous vertebra. In the cervical region they are narrow elastic bands, and 

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

 downward and backward. 



The intertransverse ligaments (Ligg. 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 fifth and sixth lumbar vertebrae and between the latter and the alse 

 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 vertebra form joints which resemble 

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



^ 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." Subcutaneous bursae may be found over the ligament at the withers. 



^ No natural line of demarcation exists between the ligamentum nuchas and the Imnbo-dorsal 

 part of the supraspinous ligament, since the change from the elastic to the white fibrous structure 

 is gradual. 



