332 THE HORSE. 
in a protuberance which is sometimes bifid. The two sides are thick and 
concave in the middle, and terminate posteriorly in a rough lip. Ante- 
riorly they form an irregular surface, having an inclination from above 
downwards, backwards and inwards. The inferior portion of this face is 
lined with cartilage, which is attached both to it and to the iium, while 
the superior has a set of strong ligamentous fibres similarly attached. 
The base looking forwards has been already described as consisting of 
three articular surfaces, above which is the spinal foramen. The apex is 
only marked by the surface of articulation with the first bone of the 
coccyx, above which is the spinal foramen, here obliquely cut and small, 
and presenting also the rudiments of oblique and transverse processes. 
THE COCCYGEAL VERTEBRZ. 
THESE BONES form the skeleton or bony basis of the tail, receiving their 
name from koxxvé, a cuckoo, whose bill was supposed to resemble this part 
in the human body. ‘They vary in number from sixteen to eighteen. In 
the first four or five all the characters of a vertebra are present, as shown 
below at a B; but these are gradually lost, and the bones at last assume 
the form of simple spines, D E F, the intermediate grade being seen at 9. 
Here there are two little processes (2), evidently abortive neural arches or 
lateral lamin, but not meeting together to form the spine. This whole 
set of bones is simply intended as a strong and flexible whip, to be moved 
by the four sets of muscles lying along, and attached to the sides of each. 
c= 
1 
BE E, D. C. B. A, 
Fia. 20.—PRoFILE View oF CoccyGEAL VERTEBRA, 
1. 1. 1. &c. Bodies. 3. 3. 3. Transverse processes. 
2. 2. 2. Spines; the lips forming the first are 4. 4, 4, &c. Fore surfaces by means of which 
joined, forming the neural arch, the the bodies articulate. 
second partially so, and the third are 5. 5. 5. Back surfaces of articulation. 
open. 
A, first ; B third: C, eighth; D, sixteenth; E, seventeenth; F, eighteenth, or last coccygeal 
vertebra. 
THE RIBS AND THEIR CARTILAGES. 
THE RIBS (Coste) have been described at page 311 as forming the lateral 
boundaries of the thorax. They are eighteen in number, of which the 
nine anterior (true or sternal) extend by means of their cartilages to the 
sternum, while the cartilages of the remainder do not extend so far, and 
they are therefore styled false or asternal. See Skeleton at page 308. 
The ribs are all long flattened bones, irregularly twisted on themselves, 
and so arranged that, when forming the wails of the thorax, they readily 
increase the volume of its contents by being drawn nearer together and 
towards the apex. In doing this they revolve upon their extremities as 
upon two centres, the superior admitting of motion from their formatior 
a3 joints, and the inferior from their elastic cartilaginous structure. 
