THE VERTEBRA IN GENERAL 365 



jaw, it grows like a tush, and has sometimes been mistaken for a second 

 tooth of that kind. Some horses are naturally formed with " pig jaws " — 

 that is to say, with the upper longer than the lower — and in these cases the 

 whole set of teeth grow to a great length, and interfere with the prehension 

 of the food. 



OS HYOIDES 



The OS hyoides in the horse consists of five distinct pieces, contributing 

 to the support of the tongue and larynx. One of these (the body) is central, 

 the other four are in pairs called the greater and lesser horns. They are 

 connected by ligaments. 



The body resembles a two-pronged fork in form, having a central portion 

 flat, an apjoendix, or spur, which lies in the centre of the muscles of the 

 tongue, and two branches. At the sides of the central portion are two little 

 knobs for the articulation of the lesser cornua. 



The horns are four in number, two short and two long; the former 

 ascend obliquely from the sides of the bodies, and end in oblong flattened 

 smooth surfaces for the attachment of the long horns. These are much 

 larger than the short horns, constituting two long, flat, thin bones, which 

 give attachment to the stylo-hyoideus and hyoideus magnus muscles, and 

 also to the constrictors of the pharynx. The bones composing the os 

 hyoides are delineated in connection with the larynx in the twenty-first 

 chapter. 



CHARACTERS OF VERTEBRiE IN GENERAL 



Every vertebra from the head to the sacrum is made up of certain 

 parts, to the uses of which in the animal economy attention has been already 

 drawn at page 350. These are — 1st, a body, which may at once be recog- 

 nized as the central and most substantial part ; 2nd, projecting upwards 

 from its upper edges are the two lamince, or sides of the ring, in which lies 

 the spinal cord ; 3rd, at the upper part of the ring is a projection, more or 

 less marked, called the spinous process ; -ith, projecting outwards from each 

 side of the body is a lateral process, intended to give insertion to muscles, 

 and in the region of the back affording a firm attachment to the ribs. In 

 addition to the connection between the bodies of the contiguous vertebrte by 

 means of a tliick fibro-cartilage, there is also a distinct articular sui-face on 

 each side of the anterior and posterior faces of the body, which is placed 

 upon a projection called the articular or oblique process. Thus, each 

 vertebra has four oblique processes, two transverse processes, a spinous 

 process, and two laminsB or sides to its large foramen, in addition to its 

 body. This last part presents an anterior and a posterior surface, more or 

 less oval, by which it is united to the next adjacent vertebrjB ; a superior 

 face, which forms tlie floor of the spinal canal, and an inferior face, which is 

 clothed with muscle on each side of a projecting x'ough line, called, wherever 

 it is marked, the inferior spine. 



Throughout the spine no two vertebrae are exactly alike, even the sixth 



