THE SPINOUS PROCESSES 



105 



middle of the back, but at the point where the legs and 

 pelvis hinge upon the spine, at the junction of tail and 

 body. In these animals the mechanism of spinal move- 

 ments is obviously of a different nature, and a whole 

 series of correlated anatomical details makes it clear that 

 no spring-like bending of the backbone takes place at or 



FIG. 36. DRAGRAM OF THE VERTEBRAL COLUMN OF AN ANIMAL. 



IN WHICH THE SPINOUS PROCESSES ARE ANTEVERTED AND 



EETROVERTED TO A DEFINITE CENTRE OF MOVEMENT. 



near its mid-point. But the pelvic anticlinal vertebra 

 is a true centre of movement in animals built upon this 

 type. Towards the fixed pelvic girdle the head and neck 

 and the whole of the trunk may be pulled, and raised, as 

 the arm of a crane; towards the same fixed point the 

 usually elongated tail may be similarly pulled up. This 

 is a simple and primitive anatomical plan, and it is 

 adapted to simple and primitive types of movement. 

 The range of body movements possible with this plan of 

 arrangement of spinous processes and their associated 

 muscles would appear to comprise such actions as crawl- 

 ing, waddling, shuffling, that type of running best termed 

 ambling, and simple aquatic paddling. 



In all these actions there is no regional bending of the 

 vertebral column, no centre of movement save that 

 situated at the point above the hips. This is the mechan- 

 ism, and these are the movements of most of the existing 



