42 PHYSIOLOGY. 



their form by their elasticity. When we stand in the erect 

 posture, the number of minute but efficient springs on which 

 the weight of the body rests, in the several joints of the back, 

 in the hip, knee, and ankle joints, infinitely surpasses the 

 powers of the human mind to calculate or even to imagine. 



9. There is a peculiar tissue, allied to ligament in its tex- 

 ture, distinguished by a high degree of elasticity, fibrous 

 structure, and tawny colour, and is hence often called elastic 

 tissue. This structure is very conspicuous in the neck of 

 those animals, which have to support a heavy load horizon- 

 talljl at the the extremity of a long neck, as in the elephant, 

 the deer, and our domestic cattle. Had their heads been 

 supported merely by muscular action, as that is liable to fa- 

 tigue and requires intervals of rest, as well as the exercise of 

 volition, the postures could not have been sustained for any 

 length of time without pain and exhaustion. This tissue, 

 which is liable to none of these objections, is accordingly 

 | substituted for muscular power, in fixing the forms, preserv- 

 ing the attitudes, and contributing to motionj The strong 

 fibrous band, stretching along the back part of the neck to 

 the head of these animals, enables them with perfect ease to 

 support the head. It is the elasticity of this membrane 

 which causes the head of these animals to be bent back after 

 death, the action of the muscles having ceased. It also re- 

 tracts and retains the sharp claws of the cat tribe within 

 their sheath when not in use. A ligament of this tissue also 

 retains the wings of birds in a bent position when they are 

 in a state of rest. 



10.-|TAe osseous fabric$The osseous or bony tissue is 

 another form of cellular matter. The bones constitute the 

 hardest and the most solid parts of the whole system, and are 

 the principal parts thatjgive it form and stability, forming as 

 it were, the frame work of the animal machine,/ The num- 

 ber of bones in the human adult, including the teeth, is; 245. 

 When we examine the broken surface of a bone, with a mi- 

 croscope/we find it abundantly supplied with minute blood- 



