FIBROUS TISSUE— PHYSIOLOGY OF MUSCLE. 269 



Chemical Composition. — The flexibility of fibrous tissue :s owing 

 to the presence of water in it, of which it contains about two-thirds 

 of its weight. A tendon or ligament will readily dry and become 

 brittle. Acetic acid causes it to swell up, and here the acid dis- 

 closes the existence of nuclei and elastic fibres. It is chiefly com- 

 posed of gelatine, which is extracted by boiling. 



Blood-vessels. — White fibrous tissue contains few blood-vessels. 

 They usually follow the course of the fasciculi ; in ligaments they 

 run in a longitudinal direction, sending off" communicating branches 

 across the fasciculi, and eventually forming an open network. 

 The periosteum is much more vascular, but the vessels do not 

 strictly belong to the membrane, as the ramifications found in it 

 are chiefly intended for supplying blood to the bone which it 

 covers. 



Nerves. — Small tendons contain no nerves, and large ones only 

 small filaments. In the periosteum, nerves are abundant; they 

 exist there chiefly for supplying the bones with sensibility. The 

 pain caused in rheumatism, which is an intensely painful disease, 

 is a proof of the sensibility of white fibrous tissue. 



PHYSIOLOGY OF MUSCLE. 



With trifling exceptions the whole of the movements of the 

 body and limbs are performed by the agency of that peculiar sub- 

 stance, known in our butchers' shops as " flesh," and recognised 

 by anatomists as muscular tissue. This constitutes the chief bulk 

 of the soft parts external to the three great cavities (the cranial, 

 thoracic, and abdominal), and in the half-starved subject of the 

 knacker or highly-trained race-horse, in which the fat has almost 

 entirely disappeared, the ordinary observer will detect nothing 

 but muscles (with their tendons) and bones beneath the skin 

 covering the limbs. On the trunk they are spread out into layers 

 varying in thickness, sometimes interrupted by flat tendons, so as 

 to form, at the same time, a protection to the organs within, easily 

 capable of extension or contraction, and a means of moving the 

 several parts upon each other. 



Tendons resemble ligamenti in being composed of white fibrous 

 tissue, described at page 268. They serve to connect muscle with 

 bone, and are useful as aff'ording an agent for this purpose of much 

 less compass than muscle itself, and also of a structure not so easily 

 injured by external violence. Thus they are generally met with 

 around the joints, the muscular substance chiefly occupying the 

 space between them. There are three varieties of tendon — 1. 

 Funicular, consisting of cord-like bands ; 2. Fascicular, including 

 bands cf a flatter and more expanded nature; and 3. Aponeurotic, 

 which are membranous, and are chiefly met with around the ab- 

 domen. The fibres are firmly attached to the bones, which s;ener- 

 23* ' n 



