48 SPECIAL ANATOMY OF THE SKELETON 



SPECIAL ANATOMY OF THE SKELETON. 



THE VERTEBRAL OR SPINAL COLUMN, OR THE SPINE 

 (COLUMNA VERTEBRALIS). 



The vertebral column is a flexuous and flexible column formed of a series of 

 bones called vertebrae. 



The vertebrae are thirty-three in number, and have received the names cervical, 

 thoracic, lumbar, sacral, and coccygeal, according to the position which they occupy; 

 seven are found in the cervical region, twelve in the thoracic, five in the lumbar, 

 five in the sacral, and four in the coccygeal. 



This number is sometimes increased by an additional vertebra in one region, or 

 the number may be diminished in one region, the deficiency being supplied by 

 an additional vertebra in another. These observations do not apply to the cervical 

 portion of the vertebral column, as the number of bones forming it is rarely 

 increased or diminished. 



The vertebrae in the upper three regions of the spine remain separate through- 

 out life, and are know r n as true or movable vertebrae; but those found in the sacral 

 and coccygeal regions are firmly united in the adult, so as to form two bones 

 five entering into the formation of the upper bone or sacrum, and four into the 

 terminal bone of the spine or coccyx. The fused vertebrae are known as false 

 or immovable vertebrae. 



With the exception of the first and second cervical, the true or movable verte- 

 brae present certain common characteristics which are best studied by examining 

 one from the middle of the thoracic region. 



GENERAL CHARACTERS OF A VERTEBRA. 



A typic vertebra consists of two essential parts an anterior solid segment, the 

 body, and a posterior segment, the arch (arcus vertebrae}, or the neural arch. The 

 arch is formed of two pedicles and two laminae, supporting seven processes viz., 

 four articular, two transverse, and one spinous. 



The bodies of the vertebrae are placed one upon the other, forming a strong 

 pillar for the support of the cranium and trunk; the arches forming a hollow 

 cylinder behind the bodies for the protection of the spinal cord. The different 

 vertebrae are connected by means of the articular processes and the intervertebral 

 fibrocartilages ; while the transverse and spinous processes serve as levers for the 

 attachment of muscles which move the different parts of the vertebral column. 

 Lastly, between each pair of vertebrae apertures (Jor.amina intervertebral ia) exist 

 through which the spinal nerves pass. 



The Body (corpus vertebrae) is the largest part of a vertebra. Its upper 

 and lower surfaces are flattened and rough for the attachment of the intervertebral 

 fibrocartilages, and each presents a rim around its circumference. In front it 

 is convex from side to side, concave from above downward. Behind it is flat 

 from above downward and slightly concave from side to side. Its anterior 

 surface is perforated by a few small apertures, for the passage of nutrient vessels; 

 while on the posterior surface is a single large, irregular aperture, or occasionally 

 more than one, for the exit of veins, the venae basis vertebrae, from the body of 

 the vertebra. 



Pedicles (radix arcus vertebrae). The pedicles are two short, thick pieces 

 of bone, which project backward, one on each side, from the upper part of the 



