98 CONTRACTILE ELEMENTS. 



is also true that the bones grow ; embryonic globules may be 

 v^yj--, seen, in their circumference, in course 



of proliferation, some bony parts dis- 

 appearing, while others make their 

 appearance. They are simply chang- 

 es of form, if we look at the skeleton 

 as a whole, but insignificant, if we 

 consider this element in particular; 

 and, in the adult stage, the bony 

 lamellaa have only physical proper- 

 ties. What is true of the bones is 

 also true of the cartilages, which 

 are really bones, only less rigid and 

 Fig. 24.- o Histoio^cai # eiement8 more elastic than what are usually 



called by that name. 



Tendons and Ligaments. The tendons and ligaments 

 are composed essentially of wavy or undulated fibres, some- 

 times interlaced with each other, but which give no appear- 

 ance of change of form, so that we may almost decline to 

 consider them as living. The part which they play is en- 

 tirely mechanical, and belongs to their powers of resistance 

 and elasticity. We find the latter property developed in 

 the highest degree in the yellow elastic tissue, which is a non- 

 collagenous variety of connective tissue ; the elastic fibre is 

 still more undulated than the cellular fibre ; it is exceedingly 

 curty (Fig. 25, b and c), and, when stretched out, makes 

 great efforts to regain its original form : the yellow or elastic 

 ligaments also serve to bring the different parts of the skele- 

 ton back into their normal positions, when they have been 

 disturbed by muscular action, whence ttie name which is 

 sometimes applied to them, passive muscles. We find this 

 elastic element always at work in the arteries, co-operating 

 with, or in opposition to, the muscles; and yet the result of 

 this incessant antagonism is the uniform circulation of the 

 blood. 



In general, wherever it is possible, yellow tissue takes the 

 place of muscle. This element, which acts like a spring, and 

 does not live like muscle and require as much nourishment, 

 whence there ensues great economy to the system (e.g., the 

 cervical ligaments of the large carnivora, the yellow liga- 

 ments of the vertebral lamina, the yellow ligaments in the 



* Transverse section of part of bone enclosing a Haversian canal (). Bony 

 corpuscles, with their anastomosing prolongations. 300 diam. (Todd and Bow- 

 man, " Physiological Anatomy of Mau." Loudou, 1845. Vol. 1, p. 109). 



