THE BONES. 



second vertebra incline slightly backward ; in the third they are more up- 

 right ; and in the succeeding ones are directed a little forward. In the last 



two they are remarkable for their 

 thickness ; in the fifth an oval-shaped 

 articular facet is observed on their 

 posterior border; in the sixth, two 

 are present one in front, correspond- 

 ing to the preceding, and one behind, 

 slightly concave, meeting a similar 

 facet on the sacrum. The fourth and 

 fifth vertebras very often correspond, 

 at their transverse processes, by 

 means of analogous facets. 1 



In the Ass, and sometimes in the 

 Mule, only five lumbar vertebrae are 

 found. According to M. Sanson, this 

 is the natural number in the Arab 

 Horse. 2 



4. Sacrum. 



The sacrum results, as already 

 stated, from the consolidation of 

 five vertebrae. This single bone 

 articulates, in front, with the last 

 lumbar vertebra ; behind, with the 

 first coccygeal bone, and on the 

 sides with the ossa innominata. It 

 is triangular, flattened above and 

 below, and from before to behind 

 describes a slight curve up- 

 wards. It offers for study a 

 superior and an inferior face, 

 two borders, a base, a summit, 

 and a central canal, the exten 

 sion of the spinal canal. 



Faces. The superior face 

 presents, on its middle, the spi- 

 nous processes of the sacral 

 vertebras, which together con- 

 stitute what is called the sacral 

 or supersacral spine. These 



LUMBAR VERTEBRA; FRONT VIEW. processes are united at their 



1, Body; 2 Its articular face ; 3 Superior spinous b j d { isolated 



process , 4, Spmai foramen ; 5, Anterior articular A . 7 ' . n .. . 



processes; 6, 6, Transverse, or costiform pro- for remainder of their ex- 

 cesses ; 7, Posterior articular process. tent ; they all incline backwards 



1 We possess the skeleton of a horse which has seven lumbar vertebrae, with the 

 normal complement in the other regions. The seventh is no doubt the first sacral, as it 

 has all its characters. The fifth sacral vertebra is evidently derived from the coccygeal 

 region. 



2 (This statement is scarcely correct. M. Sanson has established the fact that there 

 is in reality no Arab horse ; and asserts thnt the specific type with five lumbar vertebnr, 

 is very probably of African origin, nnd that these vertebrae, independently of their number, 

 offer individual characteristics different from those observed in the vertebrae of the type 

 which has six.) 



UPPER SURFACE OF LUMBAR VERTEBRJE. 



1, Summit of spinous process -, 2, 2, Anterior 

 articular processes; 3, 3, Posterior articu- 

 lar processes ; 4, 4, Transverse processes. . 



Fig. 16. 



