Morphometry, histochemistry, and innervation of cervical shoulder muscles in the cat.

Morphometric and histochemical methods were used to estimate the force-developing capabilities and fiber-type contents of four muscle complexes (rhomboideus, levator scapulae, trapezius, and sternomastoideus) that link the shoulder girdle to the skull and cervical vertebrae. Each complex contained at least two member muscles that were distinctive architecturally and often had specialized innervation patterns. Trapezius and sternocleidomastoideus were innervated by both cranial nerve XI and cervical spinal nerves. Glycogen depletion of trapezius suggested that the nerves derived from cervical roots might be entirely sensory. Muscles within each complex varied in physiological cross-sectional area from less than 0.1 cm2 to greater than 1 cm2. They showed differences in fiber-type composition that suggested specialized roles for different behaviors. The morphometric features of the cervical shoulder muscles suggest that they have considerable potential to produce head movements and should be incorporated into feline head-movement models.