Sentence:  If you attentively regard almost any quadruped's <WSD>spine</WSD>, you will be struck with the resemblance of its vertebrae to a strung necklace of dwarfed skulls. 
Meaning of the word marked with <WSD> tags:  The series of bones situated at the back from the head to the pelvis of a person, or from the head to the tail of an animal; backbone, vertebral column.