THE VERTEBRA. 43 



MoMity of the Spine. — In the cervical region, the almost total absence of 

 spinous processes, the great development of the articular processes, and the very 

 short curve described by the surfaces of contact of the vertebral bodies, allow 

 the spine very extensive and varied movements. In the dorsal region, however, 

 these movements are very limited, the spinous processes and the costal arches 

 preventing the play of the vertebrae on each other. In the lumbar region, the 

 spine can be flexed and extended more than in the dorsal ; but its lateral move- 

 ments are quite as restricted, owing to the presence of the transverse processes and 

 the reciprocal union or dovetailing of the articular processes. Lateral motion is 

 even rendered impossible in the posterior half of this region, from the manner 

 in which the transverse processes are adapted to each other. It may be remarked, 

 however, that this disposition singularly favours the integral transmission of the 

 propulsive efforts communicated to the trunk by the posterior extremities. 



The sacral vertebrae, having to afford the ossa innominata a solid fixed point, 

 could not preserve their independence and mobility if they were like the other 

 vertebrae ; they are consequently consolidated into a single piece, which fulfils all 

 that is required of it in this respect. In the coccyx the spine again recovers its 

 mobility, and to an extent more marked than elsewhere ; the bones, articulating 

 with each other by means of convex surfaces, and having no long processes at 

 their extremities, are placed in the best possible conditions for effecting varied 

 and extensive movements. 



Varieties in the Vertebral Column. 



To anatomists, the bones of the spine have frequently offered curious varieties 

 in their shape and number. 



1. Shape. — Goubaux has observed varieties of this kind in the last two cervical 

 vertebrae of the Horse. In one instance, the sixth had the transverse process 

 biscuspid on the left and tricuspid on the right. This anatomist has collected 

 several similar examples. Husson has found the sixth cervical vertebra with a 

 prolongation deficient in the transverse processes ; and the seventh, on the con- 

 trary, with an additional prolongation. 



The dorsal vertebra have also exhibited varieties in shape. Daubenton has 

 referred to the skeleton of an Ass, in which the last vertebra had on one side 

 only a transverse process like that of the lumbar vertebrae. We have seen this 

 variation in the Horse. 



In the lumbar region, Goubaux has noticed — as we have done — the fourth and 

 fifth vertebrae sometimes articulating by their transverse processes ; the articula- 

 tions may even be fused. Sometimes the transverse processes of the first lumbar 

 vertebra articulate at their base with the body of the bone, and become floating 

 ribs. 



Thomas has remarked an interesting variation in the sacrum. He found in 

 the Sheep a long, costiform, transverse process on one of the sides of the first 

 sacral vertebra. The last vertebra in this region sometimes shows, in the Dog — • 

 either to the right or left, or on both sides at the same time— one or more articular 

 facets on the transverse processes, uniting with similar facets on the first coccygeal 

 bone (Goubaux). 



2. Number. — For a long time, instances have been accumulating of variations 

 in the number of bones in the spine ; but they do not form a very imposing 

 array, probably because it is difficult to observe them without making a special 

 and attentive study of the subject. 



