THE HORSE IN MOTION. 27 



is inapplicable to them. The word " spine " is also objectionable, 

 as it is derived from the processes which superficially mark its 

 course. There seems to be no objection to the term " vertebra," as 

 a collective noun applied to the whole or any number of its parts. As 

 it is the keel and connection of the various parts of the animated 

 engine, so it is the term from which has been derived the name for the 

 whole divi>ion of animals to which quadrupeds belong, Vertebrates. 



The vertebra of the horse is divided into five groups, differing ma- 

 terially in their mechanical, even more than in their physiological rela- 

 tions. These groups are the Cervical, the Dorsal, the Lumbar, the 

 Sacral, and, lastly, the Caudal. The cervical vertebras have an im- 

 portant relation to locomotion, second to no other division. They are 

 provided with spines along the median plane, as are all the vertebrae, 

 and transverse projections or processes, which afford attachments to 

 ligaments to maintain their relative positions ; and with important 

 muscles, as will be shown in a subsequent chapter. There is great 

 freedom of motion of these bones upon each other, in comparison 

 with those of the next two divisions, especially at the articulation with 

 the head and the first vertebra of the trunk. This last is a ball and 

 socket joint of a peculiar construction, to enable the animal to reach 

 the ground, as in grazing and drinking. 



The second group is the dorsal, and it consists of those vertebras 

 that are articulated with the ribs. Like the cervical, these are pro- 

 vided with transverse processes, which serve not only for muscular 

 and ligamentous attachments, but as braces to the ribs. The spinous 

 processes are longer than those of any of the other vertebras, especially 

 along the withers, where the suspending muscles of the anterior extrem- 

 ity originate. It will be apparent to the most superficial observer that 

 the motion, either lateral or vertical, of the dorsal vertebrae upon each 

 other is very circumscribed, being limited in a vertical direction by the 

 long spinous processes and their intermediate inelastic ligaments, and 

 in a lateral direction by the transverse processes and their articulating 

 ribs. The next division is that of the lumbar region, or the vertebras 

 of the loin, with which there are no connecting ribs. As the former 

 group was more intimately related to the thorax, so those of the lum- 



