THE VERTEBRA. 45 



region ; and in the second, the augmentation in the lumbar region has been com- 

 pensated for by a diminution in the coccygeal region. 



These transpositions occur more especially on the confines of the dorso-lumbar 

 and lumbo-sacral regions. 



But the increase or decrease in the normal number of vertebrae is sometimes 

 absolute. Goubaux and Husson have found, in the Horse, nineteen dorsal 

 vertebrae with the normal number of the other vertebrae. The Ass with twenty 

 ribs already mentioned, had the usual number of vertebras in the other regions. 

 The first-named anatomist has counted, under the same conditions, seven lumbar 

 vertebrae in the Sheep. Hering, Rueff, Leyh, Sanson, etc., have found five lumbar 

 vertebrae in the Horse, without any modifications in any other parts of the 

 vertebral column. Sanson has even remarked, that in several oriental Horses 

 there are generally only five lumbar vertebrae. The presence of this anomaly is 

 always allied to a particular shape of the cranium and face. In the estimation 

 of Sanson, these characters are so important that they serve to distinguish specific 

 types. The specific type with five lumbar vertebrae is pecuHar to north-east 

 Africa, probably Nubia, 



It is not intended in this place to discuss the opinions of Sanson and the 

 value of his specific types, but merely to remark that the number of vertebrae is very 

 liable to variation in each region of the spine, and that these variations are even so 

 frequent in animals of the same origin, that it would be perhaps premature to 

 attribute to the number of vertebra in a given region the value of an absolutely 

 specific character. 



It has been attempted to explain these variations by an ancestral influence, 

 or by the influence of surroundings and exercise. But why might they not be 

 the consequence of irregularities in the fusion of the nuclei which constitute the 

 vertebral column of the foetus ? Fol has observed that at the fifth week the 

 human embryo has thirty such pieces, and that at the sixth week the thirty- 

 eighth, thirty-seventh, and thirty-sixth vertebrae have become one, while the 

 thirty-fifth has no longer perfect limits — so that an embryo measuring nineteen 

 millimetres has only thirty-four vertebrae. The spine of the embryo is com- 

 posed, therefore, of a larger number of pieces than that of the adult. The 

 reduction in number is due to fusions ; consequently, it is reasonable to admit 

 the possibility of variations in the extent of these fusions and the places where 

 they may occur. (For further details, see the Memoirs of Goubaux and Sanson, 

 in Robin's Journal de VAnatomie de la Physiologie, 1867 and 1868.) 



Comparison of the Vertebral Column of Man with that of the Domesticated 



Animals. 

 The vertebral column of Man is composed of twenty-nine bones : twenty -four vertebrae, 

 the sacrum, and four pieces constituting the coccyx. The twenty-four vertebrae are thus 

 distributed : 



Cervical vertebrae 7 



Dorsal „ 12 



Lumbar „ 5 



In all these vertebrae, the bodies are slightly excavated at the two extremities, while in the 

 domesticated animals, the superior or anterior is convex, and the inferior or posterior concave. 



1. Cervical vertebrae. — These are wide and short. The spinous processes are moderately 

 developed and bifid at their summits ; the transverse processes are also divided into two 

 branches — a posterior and an anterior. 



2. Dorsal vertebrx.—ln these vertebrae, the bodies increase in thickness from the first to 

 the last. In the first as well as in the last dorsal vertebrae, the spinous process is almost 



