THE LUMBAR VERTEBRM 



37 



The first thoracic vertebra is a transitional vertebra. The body in its general 

 conformation approaches very closely the seventh cervical, in that the greatest 

 diameter is transverse, its upper surface is concave from side to side, and its lateral 

 margins bear two prominent lips. On each side is an entire pit, close to the upper 

 border, for the head of the first rib, and a very small pit (inferior costal pit) below 

 for the head of the second rib. The spinous process is thick, strong, almost hori- 

 zontal and usually more prominent than that of the seventh cervical, an important 

 point to remember when counting the spines in the living subject. Occasionally 

 the transverse process is perforated near the root. 



The ninth has superior costal pits, and usually no inferior; when the inferior 

 pits are present, this vertebra is not exceptional. 



The tenth usually has an entire costal pit at its upper border, on each side, but 

 occasionally only a superior costal pit. It has no lower pits and the pits on the 

 transverse processes are usually small. 



The eleventh has a large body resembling a lumbar vertebra. The pits are on 

 the pedicles and they are complete and of large size. The transverse processes are 

 short, show evidence of becoming broken up into three parts, and have no pits for 

 the tubercles of the eleventh pair of ribs. 



In many mammals, the spines of the anterior vertebrae are directed backward, and those 

 of the posterior directed forward, whilst in the centre of the column there is usually one spine 

 vertical. The latter is called the anti-clinal vertebra, and indicates the point at which the 

 thoracic begin to assume the characters of lumbar vertebrae. In man the eleventh thoracic is 

 the anti-clinal vertebra. 



The twelfth resembles in general characters the eleventh, but may be distin- 

 guished from it by the articular surfaces on the inferior articular processes being 

 convex and turned laterally as in the lumbar vertebrse. The transverse process 

 is rudimentary and tripartite, presenting for examination three tubercles, superior, 

 inferior, and lateral, which correspond respectively to the mammillarj^, accessory, 

 and transverse processes of the lumbar vertebra. There is one complete pit on 

 the root (pedicle) for the head of the twelfth rib. 



A pecuharity, more frequent in the thoracic and lumbar than in the cervical and sacral 

 regions of the column, is the existence of a half -vertebra. Such specimens have a wedge-shaped 

 half-centrum, to which are attached a lamina, a transverse, superior, and inferior articular, and 

 half a spinous process. As a rule, a half-vertebra is ankylosed to the vertebrae above and below. 



( 



THE LUMBAR VERTEBRAE 



The lumbar vertebrae (figs. 41, 42) are distinguished by their large size and by 

 the absence of costal articular surfaces. 



The body is somewhat reniform, vnih the greatest diameter transverse, flat 

 above and below, and generally slightly deeper in front than behind. The roots 



Fig. 41. — A Lumbar Vertebra. 



(Side view.) 



Superior articular process 



MammiUary process 

 Transverse process 



Accessory process 



Inferior articular process 



(pedicles) are strong and directed straight backward, and the lower vertebral 

 notches are deep and large. The laminae are shorter and thicker than those of 

 the thoracic or cervical vertebrae, and the vertebral foramen is triangular, ^dder 

 than in the thoracic, but smaller than in the cervical region. The spinous process, 



