THE SACRUM. 31 



n* the posterior dorsal spine, and have sharp anterior and posterior 

 edges, with rough expanded extremities ; they increase slightly in 

 height, and diminish in strength backwards. 



The Transverse processes, longer than the corresponding pro- 

 cesses in any other region, are broad and flat, with rounded 

 extremities, and extend nearly horizontally from the bodies ; 

 the central are the largest, the first two inclining a little back- 

 wards, and the last three slightly forwards. The last two of 

 these processes articulate with each other by means of facets, and, 

 in advanced age sometimes become united by ossification, the 

 sixth articulating in a similar manner with the sacrum. The 

 oblique processes project farther from the arch than those of the 

 dorsal region ; the articular facets of the anterior ones are 



O * 



concave and directed inwards, while those of the posterior are 

 convex and directed outwards. 



The first four lumbar vertebras have six, the typical number of 

 articular surfaces, the fifth' having in addition one on each posterior 

 border of its transverse processes, and the sixth one on each 

 border, anterior and posterior, of these processes, or ten in all. 



FALSE VERTEBRAE. 

 THE SACRUM. 



(PL. I. H.) 



This, the bone of the croup, is a single, somewhat triangular- 

 shaped bone, consisting of five false vertebras united, in the young 

 animal by articulation, and in the adult by ossification ; it con- 

 tains the continuation of the spinal canal, forms the roof of the 

 pelvis, and has articular surfaces by which the pelvic arches are 

 attached, and in the horse these are the only articular connec- 

 tions between the axial and appendicular skeletons. Its direction 

 varies somewhat according to the breeding of the animal : in 

 lightly-made, highly-bred, and well-formed animals its long axis 

 is usually placed in a nearly horizontal line, while in horses of 

 coarser breed its coccygeal extremity is often considerably lower 

 than the other, thus giving a drooping appearance to the contour 

 of the croup. It presents for consideration superior and inferior 

 surfaces, two lateral borders, and anterior and posterior extremities. 



The superior surface is irregularly convex, with the flat-topped 

 spines of its vertebral segments running along its centre, decreas- 

 ing in height, but increasing in breadth as they extend backwards. 



