OF THE VERTEBRAL COLUMN. 223 



muscles in making passive motion for instance, at the wrist after Colles's fracture. 

 If the fingers be extended, the wrist can be flexed to a right angle. If, however, 

 they be first flexed, as in " making a fist," flexion at the wrist is quickly limited to 

 from forty to fifty degrees in different persons, and is very painful beyond that 

 point. Hence passive motion here should be made with the fingers extended. 

 In the leg, Avhen flexing the hip, the knee should be flexed." Dr. Keen further 

 points out that " a beautiful illustration of this is seen in the perching of birds, 

 whose toes are forced to clasp the perch by just such a passive ligamentous 

 action so soon as they stoop. Hence they can go to sleep and not fall off the 

 perch." 



The articulations may be arranged into those of the trunk, those of the upper 

 extremity, and those of the lower extremity. 



ARTICULATIONS OF THE TRUNK. 



These may be divided into the following groups, viz. : 



I. Of the vertebral column. VII. Of the cartilages of the ribs with 



II. Of the atlas with the axis. the sternum and with each other. 



III. Of the atlas with the occipital bone. I VIII. Of the sternum. 



IV. Of the axis with the occipital bone. IX. Of the vertebral column with the 

 V. Of the lower jaw. pelvis. 



VI. Of the ribs with the vertebrae. X. Of the pelvis. 



I. Articulations of the Vertebral Column. 



The different segments of the spine are connected together by ligaments, which 

 may be divided into five sets: 1. Those connecting the bodies of the vertebrae. 

 2. Those connecting the laminae. 3. Those connecting the articular processes. 

 4. Those connecting the spinous processes. 5. Those of the transverse processes. 



The articulations of the bodies of the vertebrae with each other form a series of 

 amphiarthrodial joints ; those between the articular processes form a series of 

 arthrodial joints. 



1. THE LIGAMENTS OF THE BODY. 



Anterior Common Ligament. Posterior Common Ligament. 



Intervertebral Substance. 



The Anterior Common Ligament (Figs. 152, 153, 160, 164) is a broad and 

 strong band of fibres which extends along the anterior surface of the bodies of the 

 vertebrae from the axis to the sacrum. It is broader below than above, thicker 

 in the dorsal than in the cervical or lumbar regions, and somewhat thicker 

 opposite the front of the body of each vertebra than opposite the interver- 

 tebral substance. It is attached, above, to the body of the axis by a pointed 

 process, where it is continuous with the anterior atlanto-axial ligament, and is 

 connected with the tendon of insertion of the Longus colli muscle, and extends 

 down as far as the upper bone of the sacrum. It consists of dense longitudinal 

 fibres, which are intimately adherent to the intervertebral substance and the 

 prominent margins of the vertebrae, but less closely to the middle of the bodies. 

 In the latter situation the fibres are exceedingly thick, and serve to fill up the 

 concavities on their front surface and to make the anterior surface of the spine 

 more even. This ligament is composed of several layers of fibres, which vary in 

 length, but are closely interlaced with each other. The most superficial or longest 

 fibres extend between four or five vertebrae. A second subjacent set extend 

 between two or three vertebrae, whilst a third set, the shortest and deepest, extend 

 from one vertebra to the next. At the side of the bodies the ligament consists of 

 a few short fibres, which pass from one vertebra to the next, separated from the 

 median portion by large oval apertures for the passage of vessels. 



The Posterior Common Ligament (Figs. 152, 156) is situated within the spinal 



