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 by a 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 



Fig. 57. The os 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 



