Page 138 - Anatomy and Physiology of Farm Animals, 8th Edition

Anatomy of the Muscular System / 123

Muscle fibers may be arranged in paral­ vane of the feather. If the fibers come from
only one side of the band, the arrangement
lel sheets, as in the abdominal muscles, or
VetBooks.ir narrower parallel bands, as in the sartorius is called unipennate; from two sides,
muscle on the medial side of the thigh;
bipennate; and from three or more sides,
muscles with fibers so arranged are called multipennate (Fig. 7‐1).
strap muscles or parallel muscles. In other The parallel arrangement of muscle
cases, the muscle fibers diverge obliquely fibers in strap muscles provides the greatest
from one another and form a rounded potential for overall muscle shortening but
muscle belly with tapered ends; this is a relatively weak arrangement, while the
arrangement is characteristic of fusiform pennate arrangement increases the power of
muscles. When individual bundles of a muscle, but at the expense of the distance
muscle fibers attach obliquely to bands of over which it can contract (Table 7‐1).
connective tissue within the muscle, vari­
ous pennate, or penniform (featherlike), Muscle Attachments
arrangements are created. In the penniform
arrangements, a connective tissue band If a muscle appears to arise directly
represents the quill and the muscle fibers from the bone, it is said to have a fleshy
attaching to it at an angle represent the attachment. In reality, the muscle fibers

Parallel fibers Fusiform Unipennate Bipennate Multipennate
“strap muscle”
Figure 7-1. Arrangements of muscle fibers.

Table 7-1. Characteristics of Muscle Arrangements
Relative Shortening Relative
Configuration of m. Fibers Potential Strength Example
Strap/ Parallel to long axis of muscle Maximal shortening Least m. sartorius
parallel
Fusiform Some fibers at an angle to long axis Somewhat less than Increased Long digital extensor
strap m. muscle
Pennate Most fibers angled relative to long Least Greatest m. triceps brachii
axis of m., attached to connective
tissue bands within m.