VERTEBRATES 



to which are attached the soft parts (e.g., the muscles), and which holds 

 enclosed in protective cavities (e.g., cranium, thorax, eye-sockets, etc.) 

 the more specially sensitive organs. 



As animals must be capable of motion, it follows that the skeleton, 

 instead of forming a single rigid mass, must consist of distinct movable 

 parts, viz., the bones. Motion takes place in the joints (name the most 

 important joints of the human body), and follows the mechanical laws 

 of levers. (In the example of the motion of the lower arm illustrated on 

 p. 4, indicate the fulcrum and the separate arms of the lever, also the 

 points of application of the power and the weight.) The bones consist 

 of two separate elements : an animal component, the cartilage, and a 

 mineral component, or bone ash. (We can separate the cartilage by 

 immersing fresh bones in dilute hydrochloric acid ; the bone ash, which 



Qoi 



HUMAN DORSAL VERTEBRA. IN THE LEFT-HAND FIGURE, SEEN FROM ABOVE ; IN THE 

 RIGHT-HAND FIGURE, SIDE-VIEW. 



K., Centrum or body of vertebra ; B., pedicle; R., foramen; D., spinous processes; Qu., 

 transverse processes ; G. , articulating process uniting vertebra to the preceding vertebra ; 

 Rg., facets for articulation of the head of the rib to the vertebra. 



consists for the most part of carbonate and phosphate of lime, may be 

 obtained by subjecting bones to a red heat.) To the mineral constituents 

 bone owes its stone-like rigidity, while the cartilaginous elements endow 

 it with the pliancy and elasticity of steel. 



A large bony rod traverses the whole length of the trunk. It forms 

 the main support of the body, and consists of a number of almost 

 similar bones, the vertebra* These are placed in front of or above each 

 other (as in man), like the stone slabs composing a pillar or column, 

 whence this rod is appropriately named the vertebral column (vertebrata). 

 It commences in the head and ends in the tail. The vertebrae are for 

 the most part more or less movably united with each other. (Explain 

 the significance of this in regard to motion.) 



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