THE VERTEBRAL COLUMN. 123 
The lumbar vertebrae (vertebrae lumbales) are seven in num- 
ber. They are large vertebrae, conspicuous for their extensive 
surfaces and processes for muscular attachment (Fig. 56, E, F). 
The transverse processes continue the general line of the ribs of the 
thoracic region. They are directed forward, as well as outward, 
and the tip of each is formed bya thin triangular plate (processus 
triangularis), which represents a fused rib. At the posterior side 
of the base of each is a short, flattened projection, the accessory 
A B 

Fic. 57. Theos sacrum: A, ventral (pelvic) surface; B, dorsal surface; 
c.v., bodies of coalesced vertebrae; f.a., auricular surface; f.s.a., anterior 
sacral foramina; f.s.m., median sacral foramina; f.s.p., posterior sacral 
foramina; p.a.s., superior articular process of first vertebra; p.m., ma- 
millary process of first vertebra; pr., promontory; p.s., spinous processes. 
process (processus accessorius). The spinous process is especially 
well-developed, and is directed forward. The articular processes 
are rotated upward, so that their surfaces are directed more 
nearly toward, or away from, the median plane, instead of to the 
dorsal or ventral surface. The anterior articular surfaces are borne 
on the bases of stout, upwardly-directed mamillary processes 
(processus mamillares). The latter are most characteristic of the 
lumbar vertebrae, but may be seen to arise in the posterior thoracic 
