THE HYOID BONE 31 



primary, exist at birth, enter into the formation of bone- 

 walled cavities, and are due to the conformation of the vertebral 

 bodies. The cervical and lumbar curves are secondary, and 

 are formed after birth. They are mainly due to a change in 

 shape of the intervertebral disks. 



Posteriorly, the spines occupy the median line or may be 

 normally twisted a little from it. In the cervical region they 

 are short and bifid, sloping backward and a little downward; 

 in the dorsal they are oblique above, more oblique in the mid- 

 portion, and nearly horizontal below; in the lumbar they are 

 horizontal. A cross-section of a cervical spine is semilunar; 

 of a dorsal, triangular; of a lumbar, oblong. On either side 

 of the spines is the vertebral groove, bounded externally in 

 the cervical and dorsal region by the transverse processes, and 

 in the lumbar by the mammillary processes. The transverse 

 processes of the atlas are long; of the axis, short, increasing 

 to the first dorsal, thence diminishing to the last dorsal, and 

 becoming suddenly much longer in the lumbar vertebrae. 

 In the cervical region the transverse processes are in front 

 of the articular processes and between the intervertebral 

 foramina. In the dorsal region they are behind both. In 

 the lumbar region they are in front of the articular processes 

 and behind the intervertebral foramina. 



The intervertebral foramina are always in front of the articular 

 processes, except those of the atlas and the upper ones of the 

 axis. They are named from the upper of the two vertebrae 

 which go to form them, excepting in the cervical region, where 

 there are eight, the fissure between the skull and atlas being 

 called the first. 



The spinal canal has three sets of openings into it, the two 

 rows of the intervertebral foramina and the intervertebral 

 fissures between the lamina. It is narrowest in those parts 

 having least motion, viz., in the dorsal and sacral regions. 

 It is round and f of an inch (17 mm.) in diameter in the dorsal 

 region; it is triangular, with the apex behind, in the cervical 

 and lumbar regions; and largest of all in the cervical regions. 



The Hyoid Bone 



The hyoid, or os linguae, is situated at the base of the tongue 

 opposite the second or third cervical vertebra, and is shaped 

 like the Greek letter 



