FASCICULI. 



Fasciculi, The fasciculi are of a prismatic figure, and their sections have 

 therefore an angular outline. The number of fibres of which they consist 

 varies, so that they differ in thickness, and a large fasciculus may be divisible 

 into two or three orders of successively smaller bundles, but of no regularly 

 diminishing magnitude. Some muscles have large, others only small fasci- 

 culi ; and the coarse or fine texture of a muscle, as recogtrized by the 

 dissector, depends on this circumstance. The length of the fasciculi is not 

 always proportioned to the length of the muscle, but depends on the arrange- 

 ment of the tendons to which their extremities are attached. When the 

 tendons are limited to the ends of a long muscle, as in the sartorius, the 

 fasciculi, having to pass from one extremity to the other, are of great length ; 

 but a long muscle may be made up of a series of short fasciculi attached 

 obliquely to one or both sides of a tendon, which advances some way upon 

 the surface or into the midst of the fleshy part, as in the instances of the 

 rectus muscle of the thigh, and the tibialis posticus. Muscles of the kind 

 last referred to are named " penniform," from their resemblance to the 

 plume of a feather, and other modifications of the arrangement, which can 

 be readily conceived, are named " semi-pen niform " and ''compound penni- 

 form." Many short fasciculi connected thus to a long tendon, produce by 

 their combined operation a more powerful effect than a few fasciculi running 

 nearly the whole length of the muscle ; but by the latter arrangement the 

 extent of motion is greater, for the points of attachment are moved through 

 a longer space. 



Fibres ; their figure and measurement. In shape the fibres are cylindrical, 

 or prismatic, and in the latter case often with some rounded surfaces and 

 angles. Their size is tolerably uniform, although fibres occur here aud there 

 in a muscle which differ greatly in size from the prevailing standard. Mr. 

 Bowman gave the average diameter in the male at -g-j-g- and in the female 

 at T ^ of an inch. According to later measurements by Kolliker in 

 different regions of the body, the prevailing size of the fibres in the muscles 

 of the trunk and limbs is from T ^ to -oo f an inch, but is less in 

 those of the head, especially in the facial muscles, in which he found the 

 diameter to range from T i^y down to -^-^Q of an inch. 



Cross stripes. When viewed by transmitted light with a sufficiently high 

 power of the microscope, the fibres, which are then clear and pellucid in 

 aspect, appear marked with fine parallel stripes or bands passing across them 

 directly or somewhat obliquely with great regularity (figs. LX. and LXI. A). 

 The stripes are commonly said to be dark, with light intervals ; but it is 

 probably more correct to speak of both light and dark stripes which alter- 

 nately cross the fibre. It must, however, be remembered that the substance 

 of the fibre is quite translucent, and, by changing the focus, the stripes 

 which at first appeared dark become light, and the previously light ones are 

 now dark. In what may be considered the definite or true focus, the dark 

 and light stripes are nearly of equal breadth, and then also may be seen, 

 very generally but not in all cases, a fine dark line passing along the middle 

 of the light stripe and dividing it into two (fig. LXI. A). This intermediate 

 line when closely examined appears to be a row of dark points. About 

 eight or nine dark and as many light stripes may be counted in the length 

 of -ro 1 ?)^ f au mcn > which would give about -j-y^^ inch as the breadth 

 of each. But whilst this may be assigned as their usual breadth, they are 

 in different parts found to be much narrower, so that not unfrequently they 

 are double the above number in an equal space. This closer approxima- 

 tion may generally be noticed in thicker and apparently contracted parts 



