VERTEBRAL COLUMN 
163 
Fic. 169.—Axis or Pia; Larerar View. 
1, Dens; 2, 2’, anterior and posterior articular 
processes; 3, posterior end of body; 4, transverse proc- 
ess; 5, foramen transversarium; 6, arch; 7, spinous 
process. Arrow indicates intervertebral foramen. 
Fic. 170.—Axis oF Pic; ANTERIOR VIEW. 
1, Dens; 2, 2’, anterior and posterior articular 
processes; 3, foramen transversarium; 4, arch; 5, spi- 
nous process. 
posterior border of the wing to the fossa under the latter, and is not visible dorsally; 
it issometimes very small or absent. The 
sides of the vertebral foramen bear two lat- 
eral projections which partially divide it 
into a ventral narrow part, which receives 
the dens, and a dorsal larger part for the 
spinal cord. In the fresh state the division 
is completed by the transverse ligament, 
which is attached to the projections. 
The axis has a large spinous process, 
which is directed upward and backward. 
The dens is a thick cylindrical rod. The 
transverse process is very small and the 
foramen transversarium is often incom- 
plete. 
The thoracic vertebre are commonly 
fourteen or fifteen in number. Their 
bodies are relatively long, constricted in 
the middle, and without ventral spines. 
Their extremities are elliptical, depressed 
in the middle, and prominent at the peri- 
phery. The arch is perforated by a fora- 
men on each side and in most of the series 
there is also a foramen in the posterior 
part of the root of the transverse process 
which communicates with the former or 
with the posterior intervertebral foramen. 
Sometimes there is a foramen in the an- 
terior part of the process also. There are 
mammillary processes except on the first 
two; in the posterior five or six vertebrae 
they project from the anterior articular 
processes. The facet for the tubercle of the 
rib is absent or fused with that for the 
head in the last five or six. The last trans- 
Fie. 171.—Sreconp anp Turrp THoracic VERTEBR® 
oF Pic; Larprat VIEW. 
Numbers around bones: 1, 1’, Anterior and poster- 
ior ends of bodies; 2, cavities for heads of ribs; 3, 3’, artic- 
ular process; 4, facet for head of rib; 5, spinous process. 
Numbers on bones: 1, 1’, Foramina of arches; 2, 2’, 
transverse processes; 3, 3’, facets for tubercles of ribs. 
