28 STRUCTURE AND ECOXOMT OF THE HORSE. 



the act of nodding ; but it scarcely admits of any lateral motion, 

 as a double movement, and too great flexibility, would have en- 

 dangered the safety of the spinal marrow, which passes from the 

 occipital hole through this bone. However, to admit the neces- 

 sary horizontal motion required by the animal, the second ver- 

 tebra is called into requisition, and its odontoid process fits into 

 a cavity in the under and posterior surface of the atlas, and 

 forms a sufficient resemblance to a ball and socket joint to allow 

 considerable lateral motion. We cannot sufficiently admire the 

 beautiful mechanism by which these important movements are 

 safely secured ; the second joint would have been as inapplicable 

 for the uses of the first as the first would be for that of the 

 second ; for if the second joint admitted vertical motion, the 

 consequence would be that the tooth-like process would be forced 

 against the spinal marrow every time the head was bent for- 

 wards ; but by the actual structure, the joint being underneath 

 the spinal cord, either a rotatory or a vertical motion can be 

 safely enjoyed. 



The remaining bones of the neck are very similar to each 

 other, their shape being very singular and irregular. They 

 liave each a large hole running through them, for the passage of 

 the spinal marrow ; a ridge on the upper part for the attachment 

 of the cervical ligament ; processes on the side for the insertion 

 of the powerful muscles that move the head and neck ; small 

 foramina or holes, for the passage of nerves and blood-vessels ; 

 and on the anterior part a round head, which is received into a 

 cavity in the back part of the bone in front of it ; also processes 

 or legs which proceed from the front part of each bone, and 

 meet and correspond with similar processes on the back part of 

 each bone. These bones, however, never actually touch each 

 other, for if they did there would be too much concussion ; but 

 between every two bones, and extending throughout the whole 

 spine, there is interposed a gristly substance, enclosed in an 

 elastic body, which yields and recoils like an air cushion. In 

 the human subject this power of dilatation exists in a very con- 

 siderable decree, owing to which men will often measure more 

 in the morning than in the evening after their daily toil is com- 

 pleted. 



Though in horses this power of dilatation is not possessed in 

 an equivalent degree, yet the elastic intervertebral substance 

 greatly contributes to the elasticity of the frame. With the 

 seven bones of the neck the spine is composed of no less than 

 thirty separate pieces, which are distinguished as the dorsal, or 

 vertebra; of the back, and the lumbar, or those of the loins. All 

 these bones have a hole through their bodies for the passage of 

 the spinal cord. Tiie dorsal vertebrae, eighteen in number, 

 are connected with each other in a manner similar to those of 



