THE VERTEBRAL COLUMN. AY 
A. The Axial Skeleton, 
I. The vertebral column or “back bone.” A bony tube 
which surrounds and protects the spinal cord: divisible into 
an anterior part which is divided transversely into nine 
rings or vertebra, and a posterior unsegmented portion of about 
equal length—the urostyle. At the sides of the tube between 
the successive vertebre are the intervertebral foramina through 
which the nerves pass out from the spinal cord to the various 
parts of the body. 
a, Structure of a vertebra. Hxamine one of the vertebre, 
say the third, more closely : draw it, showing :-— 
i. Its ring-like shape: the central neural canal in 
which the spinal cord lies. 
ii. The centrum or body: the thickened ventral por- 
tion of the ring: it articulates with the centra of 
the vertebree in front of and behind it ; and forms 
the floor of the neural canal, 
iii, The neural arch: the lateral and dorsal portions 
of the ring: forming the sides and roof of the 
neural canal. 
iv. The spinous process or neurapophysis: a small 
_ blunt median process projecting upwards and 
backwards from the top of the neural arch. 
v. The transverse processes: a pair of large lateral 
processes projecting horizontally outwards from 
the sides of the neural arch. 
vi. The articular processes or zygapophyses: on the 
anterior and posterior borders of the neural arch : 
they articulate with corresponding processes on 
the vertebree in front and behind, and so serve 
to link the vertebree together. 
a. The anterior articular processes or prezy- 
gapophyses: look upwards and slightly 
inwards. 
(. The posterior articular processes or post- 
zygapophyses : look downwards and slightly 
outwards. 
