u'SO OSTEOLOGY. 



An ordinary dorsal vertebra has twelve articnlar surfaces — viz., 

 three anterior and three posterior, as in the cervical, and three 

 at each side ; of the latter, two are for the heads of two ribs, 

 «ind the third for the tubercle of the anterior rib. The depres- 

 sions for the heads of the ribs are deepest between the anterior 

 vertebrae, and gradually grow shallower, in the two last becoming 

 continuous with the facet on the transverse process. The 

 eighteenth segment, being attached to but one rib on each side, 

 has eight articulating surfaces only. 



Viewing the dorsal vertebrae in connection, it is seen that the 

 spines diminish from the fifth backwards, and the vertebrae 

 themselves grow narrower. The first exhibits some of the 

 characters of a cervical vertebra, and the second has a short 

 body, with transverse and anterior oblique processes formed 

 on the same bony projection, and a neural spine, short, convex 

 anteriorly, and more bent than any other in the vertebral chain. 

 The first thirteen form the skeleton of the withers, and, when 

 well developed, the height of their spines increases the surface for 

 muscular attachment, and also affords greater leverage. ^^^ 



LUMBAR VERTEBRAE. L ^ ^^ 



(PL. LG.) ^-^ KrO"^^ 



These form the skeleton of the loins, and are shorter in the 

 horse in proportion to his size, than! in other animals. Their 

 number is six usually, sometimes five, in the horse, siz in the 

 mule, generally five in the ass, and also, it is said in the Arab 

 horse. Their bodies, intermediate in length between the cervical 

 and the dorsal, are thick and strong, the three anterior being 

 flattened superiorly and laterally, and possessing a strongly- 

 developed median ridge ; the three posterior ones are convex 

 laterally, and flattened above and below. More motion being 

 required in the loins than in the back, the anterior extremities 

 of the centra of the lumbar vertebrae are more convex, and the 

 posterior extremities more concave than those in the dorsal 

 region. The arches enclose a large semicircular spinal canal, 

 and with one or two exceptions possess both anterior and posterior 

 notches. The neural spines are strong, broad, and flattened 

 laterally ; they incline slightly forwards, are about the same length 

 as the posterior dorsal spine, and have sharp anterior and posterior 



