INTRODUCTORY. 11 



For convenience of description anatomists, wlien possible, 

 distinguish surfaces of hones, and the lines of union of the 

 surfaces constitute the borders. 



We have mentioned ligaments of various kinds entering 

 into the formation or perfection of joints. These are gene- 

 rally composed mainly of white fibrous tissue ; some contain 

 a small amount of yellow elastic tissue ; others mainly con- 

 sist of yellow elastic tissue, as ligamentum nuchse. We 

 have seen, too, that the ligaments are either broad expan- 

 sions or dense bands. Analogous in structure are the 

 fascise, which are found in particular regions ; they con- 

 sist of widespread membranous layers of white fibrous 

 tissue, which form sheaths to bind down muscles in their 

 situations and to brace them for action ; they are generally 

 attached to the most prominent portions of the basement 

 structures in the neighbourhood. They present channels 

 and foramina through which vessels and nerves pass, and 

 in some cases have muscles acting upon them, as tensor 

 vaginae femoris. They are most marked in those situa- 

 tions in which the muscles are long, as in the limbs. On 

 approaching an annular or a capsular ligament they blend 

 with it. The most important are fascia lata of the fore- 

 arm, the lumbar, psoas, and gluteal fascise, and the fascia 

 of the thigh. The gluteal presents a considerable amount 

 of yellow elastic tissue. Fascia superficialis abdominis is 

 wholly elastic. The several portions of the skeleton are 

 caused to move upon each other by the action of muscles. 

 The motion found in other parts of the body, with the 

 single exception of that produced by ciliae, is also due to the 

 peculiar property of muscular fibres ; this motion may be 

 voluntary or uncontrolled hy the ivill, and is brought about 

 by the contractility of two forms of fibres, voluntary or 

 striated, involuntary or unstriated. Involuntary muscular 

 fibre is that which produces the motion of most of the 

 internal organs by which nutrition and reproduction are 

 brought about ; it is generally arranged so as to form a 

 thin coating to a hollow organ or a tube or a vesicle, and 

 consists of a number of fusiform or spindle shaped nuclea- 

 ted cells overlapping each other at their extremities where 

 they meet. The double wall of separation becomes ab- 

 sorbed and thus a plain fibre is produced, distended at 

 intervals in consequence of the presence of the nucleus; 

 these fibres are collected together to form fasciculi, which 



