10 



VERTEBRAL COLUMN. 



extremity termed the head, and a narrower lower part or neck. It presents 

 in front a smooth surface for articulation with the atlas, and behind, a 

 smooth groove to receive the transverse ligament of the atlas. The study 



Fig. 7. 



Fig. 7. THE Axis VERTEBRA. ^ 



A, seen from above and behind ; B, seen from the 

 right side. 1, the body; 4, the vertebral ring 

 or foramen; 5, the spinous process, bifid and very 

 large ; 6, the transverse process ; 7, the superior 

 articulating process ; 7', the inferior oblique articu- 

 lating process ; I* in A, is placed at the side of the 

 odontoid process ; in B, in front of it, marking the 

 smooth surface of articulation with the anterior arch 

 of the atlas. 



of development appears to show that the 

 odontoid process is in reality the body of 

 the atlas anomalously connected with the 

 vertebra dentata. The superior articular 

 surfaces, placed, like those of the atlas, in 

 front of the intervertebral groove, lie on the 

 sides of the base of the odontoid process, 

 partly on the body and partly on the arch of 

 the vertebra. These surfaces look upwards 

 and slightly outwards, and are of considerable 



size ; they receive the weight of the head transmitted through the lateral 

 masses of the atlas. The inferior articulating processes, separated by a notch 

 from the body, are similar in form and position to those of the succeediug 

 vertebrae. 



The spinous process is very large, rough, and deeply bifid, affording 

 attachment to several muscles, and is grooved on its inferior surface. The 

 plates which support it are of proportionate size and strength. 



The transverse processes are short, and are scarcely grooved or bifurcated. 

 The foramen at the root of each is inclined obliquely downwards and 

 inwards. 



THE FIXED OR UNITED VERTEBRAE. 



THE SACRUM. 



The sacrum (os sacrum) is placed below the last lumbar vertebra, above 

 the coccyx, and beween the ossa innominata, and forms the upper and 

 back part of the pelvis. It consists in early life of five vertebrae, which 

 in the adult are united into one bone. The first of the five is the largest 

 vertebra in the column ; those which follow become rapidly smaller, and 

 the fifth is rudimentary. Hence the sacrum is massive above and slender 

 below, and is triangular in general form, with its base directed upwards. 

 It is concave and smooth in front, convex and uneven behind. The 

 direction of its surfaces is very oblique, its pelvic aspect looking downwards 

 and forwards, and forming at the place where it meets with the last lumbar 

 vertebra the projection termed promontory. It presents for consideration 

 a pelvic, a dorsal, and two lateral surfaces, a base and an apex, together 

 with the sacraL portion of the spinal canal. 



The pelvic surface is concave from above downwards, and slightly so from 

 side to side. It is marked across the middle by four transverse lines or 



