The coccygeal vertebrae vary considerably in number from 18 to 20.
These gradually diminish in size from the first to the last.
The first five or six are typical vertebrae but beyond the sixth the processes and the arches get gradually suppressed so that the posterior ones are made up of bodies only.
The transverse processes are relatively large.
The ventral surface presents a pair of processes -the haemal processes and between these is a groove – the sulcus vasculosus for the middle coccygeal artery.
The articular processes do not carry facets.
The arch disappears from the sixth backwards and the rudiments of the transverse processes disappear after the 9th or 10th.
Sheep and Goat
Vary in number from three (in short tailed sheep) to twenty-four or more. No haemal process on the ventral surface.
Horse
15-21 in number, An average is 18.
The laminae fail to meet dorsally after the fourth so that the neural arch is incomplete.
Pig
It is characterized by the presence of functional articular processes on the first four or five beyond which these become non-articular and smaller.
The arches of the first four or five are complete.
Fusion of the first coccygeal vertebra with the sacrum is not uncommon.
Dog
20 to 23 in number.
Neural rings are present in the first six.
The first three or four have articular processes which form joints.
Haemal arches or chevron bones in the form of a V or Y occur ventrally at the inter-central junctions of the third, fourth and fifth usually.
Rabbit
They are 16 in number.
Neural arch is complete in the first seven vertebra.
Fowl
They are seven in number. The first one is fused, with the lumbo-sacrals. The last is a three-sided pyramid called pygostyle, which results from the fusion of three or four vertebrae in the embryo and forms a foundation for the feathers of the tail and coccygeal glands. Its apex projects upward and backward
The intermediate ones are typical vertebrae.
The transverse processes of these are well developed and the spines are bifurcated.
