THE VERTEBRAE. 



37 



Fig. 22. 



According to Sanson, five is the natural number of lumbar vertebrae in the 

 specific type of African Horses (see remarks on the Spine in General). The 

 transverse processes in these animals also offer some peculiarities. Thus the 

 increase in their length ceases at the second, and from this an almost insensible 

 diminution occurs to the fifth. The transverse processes of the first lumbar ver- 

 tebra are alone less inclined backward ; they are perpendicular to the direction 

 of the body in the second and fhird, and inclined forward in the four fh and fifth. 



The thoroughbred English Horse has sometimes five, sometimes six lumbar 

 vertebme, but in every instance the 

 lumbar region is comparatively short 

 (Cornevin). 



Ass. — The lumbar vertebrae in the 

 Ass, five in number, are easily distin- 

 guished from those of the Horse by the 

 characters special to their spinous and 

 transverse processes, and articular 

 tubercles. 



1. The spinous processes are propor- 

 tionately longer that those of the Horse, 

 and they are also more inclined forward. 

 If their bodies rest on a horizontal plane, 

 and if a line be drawn tangent to the 

 posterior border of the spinous process, 

 an acute angle is always obtained at the 

 point of junction of the line and plane ; 

 but if this be done with the vertebrse of 

 the Horse, there is at least a right angle. 



2. The transverse processes increase 

 in length from the first to the second ; 

 they are nearly equal in the second and 

 third, and decrease suddenly in the fifth. 

 They are usually inclined downwards ; their posterior border and superior face, 

 near the body, are marked by a vasculo-nervous furrow, which is scarcely visible 

 in the Horse. Finally, it is not rare to find no inter-transverse articulation 

 between the two last. 



3. The most important differential character is observed in the articular 

 tubercules. The diarthrodial facets are surmounted by a flat tongue of bone, 

 which is projected outwards in the direction of the summit (see Fig. 23, A, B, 4, 

 4). This piece gradually becomes lower from the first to the fifth vertebra ; in the 

 Arst, it projects beyond the articulation by more than one-fourth of an inch, and, 

 up to a certain point, resembles the condition observed in the Rabbit or Dog. 



In the Mule there are sometimes six, sometimes only five, lumbar vertebrae. 

 These have the spinous and transverse processes somewhat as in the Horse ; their 

 articular tubercles resemble those of the Ass. 



In the Hinny, of which opportunity has rarely been had for study, Goubaux 

 and ourselves have found five lumbar vertebrse, which, in their shape, much 

 resembled those of the Ass. 



UPPER SURFACE OF LUMBAR VERTEBR/E. 



1, Summit of spinous process ; 2, 2, anterior 

 articular processes ; 3, 3, posterior articu- 

 lar processes ; 4, 4, transverse processes. 



Differential Characters in the Lumbar VERTEBRiB of other Animals. 



A. Ox, Sheep, and Goat.— The six lumbar vertebrae of the Ox are longer and thicker 

 than those of the Horse. The transverse processes are also generally more developed, aro 



