358 THE HORSE. 
ligament. On cutting through these the following sets of fibres will be 
made apparent :—Fvrst, a transverse band arises from the root of the 
odontoid process, and dividing into two like the letter V, is attached on 
each side to the ridge on the inferior part of the ring of the atlas—a few 
thin fibres passing on to be attached to the basilar process and condyles 
of the occiput. Secondly, a strong band arises from the point of the 
odontoid process, and is attached to the middle of the ridge on the 
inferior part of the atlas. Thirdly, a few fibres pass across from the 
inside of the ring of the atlas on one side to the corresponding part of 
the other. These serve to strengthen the capsule, but they have not the 
substance of the corresponding ligament in the human frame. 
MOVEMENTS OF THE VERTEBRA IN GENERAL AND OF 
CERTAIN OF THEIR JOINTS IN PARTICULAR. 
THE AMOUNT OF MOTION between any two vertebre is extremely limited. 
with the exception of the atlo-axoid articulation, in which the degree 
of rotation is considerable. But when the spine is viewed as a whole, 
these slight individual movements multiplied together are sufficient to 
allow of flexion and extension, as well as of inclination to either side. 
In the region of the back the joints are rigid, in the loins less so, but in 
the neck and tail great liberty is allowed. Flexion and extension, as well 
as lateral motion, are dependent entirely upon the elasticity of the inter- 
vertebral substance, which allows of one part being compressed while the 
other is extended. Thus, when the loins are arched upwards, the lower 
edge of this substance is compressed, while the upper part assumes a 
more expanded condition, and at the same time the spinous processes are 
separated more widely, and their ligaments are stretched. The reverse of 
this takes place when these bones are arched downwards, while in lateral 
inclination the sides are compressed and expanded in a corresponding 
manner. Very slight rotation of the whole spine, or more properly 
twisting, is permitted by the elastic nature of the intervertebral substance ; 
but in the atlo-axoid articulation a perfect rotation occurs around the 
centre of the odontoid process, allowing the muzzle to be turned in either 
direction, which could not be done without an arrangement of this 
nature. The capsular ligaments and the superior and inferior atlo-axoid 
ligaments are necessarily lax to allow of this motion. Lastly, the great 
ligament of the neck serves to support the weight of the head, which 
would be too great for the muscles of the neck, in consequence of the 
length of leverage which is presented. 
THORACIC ARTICULATIONS. 
THE ARTICULATIONS which unite the bones composing the thorax may be 
divided jirst into costo-vertebral articulations, or those which unite the 
ribs with the spine ; secondly, chondro-costal, or those which unite the ribs 
with their cartilages ; thirdly, the chondro-sternal, or those which unite 
the cartilages with the sternum ; fowrthly, the articulations of the costal- 
cartilages among themselves. 
Eacu Rib (with the exception of the first and last) is connected with 
the bodies of two vertebre, the three bones, together with the inter- 
vertebral substance, forming two joints which are separated from each 
other by a band of fibres passing from the head of the rik to the inter- 
vertebral substance. Besides these there is also an articulation between 
the rib and the transverse process of the vertebra behind it. 
