Axial Musculature vs. Appendicular Musculature

- include the skeletal muscles of the trunk and tail

- extend forward beneath the pharynx as hypobranchial muscles and muscles of the tongue

- they are also present in orbits as extrinsic eyeball muscles

- they are metameric in fish and aquatic amphibians and are used in locomotion

- in tetrapods, metameric properties cannot be seen due to the presence of paired appendages

axial musculature consists of a series of segments known as myomeres or myotomes

are separated by a sheet of connective tissue called myosepta; collagen is arranged in a grid-like formation which gives it the ability to bend laterally but not longitudinally. This gives fish the ability to move its body from side to side

into dorsal and ventral masses by horizon septum

epaxials= above the septum

hypaxials= below the septum

like fish, they have epaxial and hypaxial masses but have a series of modifications to their axial muscle system

modifications: epaxials and hypaxials

are elongated bundles that extend through many body segments and are located below the expanded appendicular muscles

hypaxials of the abdomen have no myosepta and form broad sheets of muscle and they are oriented into oblique, rectus, and transverse bundles

Lie along the vertebral column, is dorsal to transverse process, adn is lateral to neural arches

extend from base of skull to the tip of the tail 

form the dorsalis trunci muscles

function in aiding with side to side movements of vertebral columns

short and long bundles arch and support the vertebral column

anterior bundles attach and move the skull

Form the muscles of the lateral body wall: external and internal oblique, transverse, and rectus muscles

Assist in locomotion, support contents of the abdomen, assist in respiration, and assist epaxials in bending the vertebral column

muscles located on girdles, limbs, and fins

extrinsic: originate on axial skeleton and insert on girdles or limbs

intrinsic: originate on girdle and insert on the distal elements

appendicular muscles are more complex in tetrapods due to the accommodation for terrestrial life

• muscles serve as stabilizers
• dorsal and ventral components of embryonic mscles bud from extensors and flexors
• paired fins operation as unjointed appendages
• the intrinsic muscles are limited in number and are undifferentiated

very complex muscle system to accomplish locomotion on land and jointed appendages (as opposed to fins)

muscles are organized as opposing groups and classified as intrinsic or extrinsic

extrinsic muscles (primitive) originate from blastemas within the body wall and insert on girdle or proximal to limb bones

intrinsic appendicular muscles originate from blastemas, located within the developing limb

extrinsic muscles of the pectoral girdle and forelimbs are divided into the dorsal group and the ventral group

dorsal group of forelimbs include muscles such as trapezius and latissimus dorsi arise on: 

• 1) fascia of trink in lower tetrapods
• 2) skull, vertebral column and ribs, behind the scapula

ventral group includes muscles such as pectoralis major and minor and the supracoracoideus (Birds), which developed into the intrinsic muscle called the supracoracoid

- most develop from hypaxial blastemas in the body wall

- it is referred to as secondary appendicular muscles because it was not their original function to operate appendages

- chief extrinsic muscles of tetrapods include: scupular deltoid, latissimus dorsi, rhomboideus, serratus ventralis and pectoralis

• form from blstemas within the limb bud
• called primary appendicular muscles

intrinsic muscles of the pectoral girdle and forelimbs are divided into the dorsal group and the ventral group

dorsal group includes muscles that arise on the scapula and insert on the humerus such as deltoideus, teres major and minor, and long head of triceps brachii

ventral group include muscles of the pectoral girdle that includes supraspinatus, infraspinatus, bicep brachii, and brachialis