This document defines and describes several key anatomical structures found in the trunk and tail region of vertebrae, including the hemal spine, hemal arch, neural spine, neural arch, notochord, centrum, diapophysis, parapophysis, prezygapophysis, and postzygapophysis. It explains that the hemal spine and arch are found on caudal vertebrae and enclose the caudal vein and dorsal aorta, while the neural spine and arch form the posterior projection enclosing the vertebral foramen. The notochord and centrum provide early support as the vertebrae develop.

1. Trunk and tail part

4.  Hemal spine
a spine extending downwards from the lower end of the
haemal arch in posterior or caudal vertebrae
 Hemal arch
the arch which encloses the caudal vein and dorsal
aorta and is found on the ventral surface of the
more posterior ( caudal ) vertebrae

5.  Neural spine
the middle point of the vertebral arch, represented by the
spinous process.
 Neural arch
the posterior projection from the body of a vertebra that
encloses the vertebral foramen.
•Notochord
a flexible rod-shaped body
first "backbones" serving as support structures
advantageous to primitive fish-ancestors because they were a
rigid structure for muscle attachment, yet flexible enough to allow
more movement than, for example, the exoskeleton of the dominant
animals of that time.
•Centrum
A part of vertebra that occupies the position occupied early in
the ontogeny by the notochord

6.  Diapophysis
the superior or articular surface of the transverse process of
a vertebra
 Parapophysis
the ventral transverse, or capitular, process of a
Vertebra.
•Prezygapophysis
The superior processes project upward from a lower
vertebra, and their articular surfaces are directed more or
less backward
•Postzygapophysis
The inferior processes project downward from a higher
vertebra, and their articular surfaces are directed more or
less forward and outward.