CAUDAL AUTOTOMY AND REGENERATION IN THE GECKO 76 
Each elongated saddle-shaped vertebra consists of an elongated 
centrum containing a notochordal canal (full of tissue not 
shown in the figures) running continuously between successive 
centra but closed at the planes of cleavage (autotomy planes), 
to be mentioned shortly. Successive centra are separated by 
intercentral pads of cartilage (perforated by the notochord), 
to which the bony haemal arches (chevron bones) are attached 
below. Midway in its length, and on the anterior side of the 
vertebral cleavage plane, each centrum gives off laterally on 
each side a large transverse process, which extends 
outwards and posteriorly to the outer surface of the sub- 
muscular fat bands. On the ventral side of each intervertebral 
joint and attached to the joint (not the centrum) is the haema] 
arc¢h which bears a median haemal spine for the attach- 
ment of muscles. Dorsal to the centrum is the neural arch 
which mid-vertebrally bears a conspicuous neural spine. 
The well-known feature of the vertebral column im the seg- 
mented region of the tail is the presence of a vertebral 
cleavage plane dividing the whole vertebra (centrum 
and neural arch) to two pieces in the middle of its length, 
each autotomy segment thus containing the two halves of two 
successive vertebrae. This vertebral cleavage plane is marked 
by a hyaline septum which is continuous with the similar 
septa marking the cleavage planes of the skin, subcutaneous 
fat layer, muscular layer, and the submuscular fat bands, and 
it is therefore obvious that, with the exceptions of the spinal 
cord, spinal nerves, caudal artery, and caudal vein, and certain 
longitudinal blood-vessels, the whole substance of the 
tail is traversed at each intersegmental 
joint by a hyaline septum marking a con- 
tinuous cleavage plane. 
Nor do the adaptations to autotomy im the various systems 
of organs cease here. Though naturally the spinal cord and 
small longitudinal nerves and blood-vessels show no signs of 
cleavage planes, yet when we examine the two big blood- 
vessels of the tail we find special mechanisms for stopping 
haemorrhage when autotomy occurs. (f) The caudal 
