Vv \A . \ - 



THE RABBIT. 67 



the epiphyses (chap, vi., 11). These epiphyses to the 

 vertebral centra occur only among mammals, and are even 

 absent in some cases within the class. In the adult rabbit 

 they have ankylosed (fused) with the rest of the centrum. 

 In a young rabbit's skeleton, they adhere more readily to 

 the intervertebral pad than to the centrum, hence at the 

 right-hand side of fig. 34 the epiphysis of the next vertebra 

 is seen adhering. 



Each thoracic vertebra is attached to its fellows in front 

 and behind by solid masses of fibre-cartilage the inter- 

 vertebral pads, which limit to some extent the possibilities 

 of bending of the vertebral column. A more important 

 limitation of such motion is afforded by the zygapophyses, 

 which are paired projections from the two ends of the neural 

 arch, so disposed that those at the posterior end of one 

 vertebra overlap those at the anterior end of the next. In 

 life these contiguous zygapophyses are involved in a synovial 

 joint, that is to say, their articulating surfaces are enclosed 

 in a chamber containing a lubricating fluid which facilitates 

 the sliding of one surface over the other. This allows a 

 limited amount of lateral bending of the vertebral column, 

 less vertical bending, and almost entirely prevents torsion 

 i.e. the unequal rotation of different vertebrae about the 

 longitudinal axis as the student who sees and understands 

 the relation of the zygapophyses will readily realize. In 

 the macerated vertebra the articular surfaces of the zygapo- 

 physes are exposed as smooth surfaces, and afford a ready 

 means of distinguishing the front and hind ends of an 

 isolated vertebra : the normals to the polished surfaces of 

 the anterior zygapophyses pointing upwards and inwards t 

 those of the posterior ones downwards and outwards. 



There are usually twelve thoracic vertebrae in the rabbit. 

 The first nine have long neural spines, pointing posteriorly ; 

 the tenth has a shorter spine which points vertically ; the 

 rest have short spines pointing anteriorly. In the ninth 

 and following ones a small process is developed from the 

 proximal end of the transverse process : this is called the 

 metapophysis and will be better seen in the lumbar verte- 

 bras. The distinguishing feature of the thoracic vertebrae 

 is the presence of ribs articulated to them. 



