AP BIOLOGY

Detailed explanation-1: -Epaxial muscles extend along the dorsal side of the transverse processes of the vertebrae. These muscles contract and cause dorsal concavity of the back and tail, pulling the fluke up in the upstroke. These muscles, especially the multifidus and longissimus, are enormous (Fig. 2).

Detailed explanation-2: -Epaxial and hypaxial muscles are defined as muscles innervated by the dorsal and ventral rami of spinal nerves, respectively. Each cluster of spinal motor neurons passing through dorsal rami innervates epaxial muscles, whereas clusters traveling on the ventral rami innervate hypaxial muscles.

Detailed explanation-3: -Some fishes rely on large regions of the dorsal (epaxial) and ventral (hypaxial) body muscles to power suction feeding. Epaxial and hypaxial muscles are known to act as motors, powering rapid mouth expansion by shortening to elevate the neurocranium and retract the pectoral girdle, respectively.