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Perineal Hypaxial Muscles

trunk. Therefore, the three inner layers of the lateral wall become the major contributors to the pelvic hypaxial wall. The three

muscle layers from each side pass into the bottom of the pelvis where they meet in the midline to surround the urethra,

vagina, and anus. This three-layered muscle fl oor at the bottom of the pelvis is called the pelvic diaphragm (internal layer)

and the perineum (middle and external layers.) The pelvic diaphragm forms a basin-shaped fl oor that supports the pelvic

viscera. The perineal muscles span the diamond-shaped pelvic outlet, and are divided into an anterior urogenital triangle

and a posterior anal triangle. The perineal muscles support the pelvic viscera, form important sphincter muscles that surround the urethral and anal orifi ces, assist in erectile function, and propel the sperm from the male penis during ejaculation.

Additional views of these muscles in both the male and female are depicted in the reproductive system chapter.

The ventral, subvertebral, and lateral supracostal

muscles are either annexed by the lower limb

or terminate above the pelvic region of the

Dissection of male perineal muscles

Inferior view

External perineal muscles

Middle perineal muscles

Internal perineal muscles

Perineal Musculature

 1 Obturator externus muscle

 2 Ischiocavernosus muscle

 3 Bulbospongiosus muscle

 4 Superficial transverse perinei muscle

 5 Superficial external anal sphincter muscle

 6 Deep external anal sphincter muscle

 7 Deep transverse perinei muscle

 8 Levator ani muscle

 9 Ischiococcygeus muscle

Other Muscles and Structures

10 Gluteus maximus muscle

 11 Penis (cut)

12 Obturator nerve

13 Ischial tuberosity

14 Coccyx

15 Perineal body

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Upper Limb Muscles

While the majority of the muscles of the upper

limb arise as true limb muscles from the embryonic somites, some of the upper limb

muscles are annexed from the body wall and head musculature to support and

stabilize the scapula and suspend it from the trunk skeleton. Th e levator

 scapulae, rhomboideus major and minor, serratus anterior, pectoralis minor,

and subclavius muscles are annexed lateral body wall muscles that help

suspend the scapula, while the trapezius is an annexed branchial arch

muscle that is also a part of the scapular group. Unlike these annexed

body wall and head muscles, the true muscles of the limb arise from

mesenchymal migrations of the somites into the developing limb

bud. Th ese migrations form two distinct muscle masses in the limb,

an anterior muscle group and a posterior muscle group. As the

limb develops, the two distinct muscle groups become separated

by connective tissue septa and bones into anterior and posterior

muscle compartments within the diff erent sections of the limb.

As the ventral rami of the associated spinal nerves grow into the

developing upper limb bud, a nerve network, or plexus, develops. From this plexus posterior divisions of the network send

branches into the posterior muscle compartments and anterior

divisions of the network send branches into the anterior muscle

compartments. At the proximal end of the limb, some of the

true limb muscles from the anterior and posterior compartments increase in size and migrate back onto the trunk. As they

spread onto the trunk, they cover the body wall muscles and

 attach to the axial skeleton. Th is muscular expansion of the proximal limb muscles increases their mechanical advantage at the

shoulder joint. Because of this interesting arrangement of body

wall muscles and true limb muscles at the shoulder end of the

 superior limb, a clear compartment organization is not evident. For

this reason, we will group these muscles into groups that share some

common feature, such as a common attachment or function. In the limb

proper we group the muscles into their developmental anterior and posterior muscle compartments. Th is greatly simplifi es the learning process

 because most of the muscles in a compartment share common attachments,

 actions, and nerves. Grouping things in this way can help to simplify the learning

process.

Find more information

about the muscles of the

upper limb in

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outer layer of the trunk wall and head to help suspend it from the axial skeleton. This scapular muscle sling, which has no

homologous counterpart in the lower limb, is the major difference between the muscles of the upper and lower limbs. On the

pages that follow we present the muscles of the upper limb and organize them primarily by developmental groups, with the

exception of the muscles of the shoulder joint (see the outline below). The opposite page and the two pages that follow show

anterior and posterior views of the upper limb muscles and their relationships to the trunk musculature.

This chapter depicts the interesting array of muscles of the

upper limb. Because of its weak ligamentous association with

the axial skeleton, the upper limb annexed muscles from the

Upper Limb Muscles

Pectoral Girdle Muscles

(Annexed from head muscles (trapezius) and outermost layer of

lateral trunk muscles to support and stabilize scapula)

 Trapezius

 Levator scapulae

 Rhomboideus major

 Rhomboiedus minor

 Serratus anterior

 Pectoralis minor

 Subclavius

Shoulder Joint Muscles

 Rotator cuff muscles

(Muscles with a ligamentous role that function as stabilizers of

the weakly ligamentous shoulder joint)

 Supraspinatus

 Infraspinatus

 Teres minor

 Subscapularis

 Intertubercular groove muscles

(Muscles that share an insertion on the intertubercular groove

and are prime movers of the shoulder joint)

 Pectoralis major

 Latissimus dorsi

 Teres major

 Deltoid

Anterior Brachial Muscles

(Nerve supply - musculocutaneous nerve; function as flexors of the

shoulder and elbow)

 Coracobrachialis

 Brachialis

 Biceps brachii

Posterior Brachial Muscles

(Nerve supply - radial nerve, like all posterior compartment muscles;

functions as extensor of shoulder and elbow)

 Triceps brachii

Anterior Antebrachial Muscles

(Nerve supply - median and ulnar nerves; function as flexors of wrist

and digits)

 Superficial muscles

 Pronator teres

 Flexor carpi radialis

 Palmaris longus

 Flexor carpi ulnaris

 Flexor digitorum superficialis

 Deep muscles

 Flexor digitorum profundus

 Flexor pollicis longus

 Pronator quadratus

Posterior Antebrachial Muscles

(Nerve supply - radial nerve; function as extensors of the wrist and

digits)

 Lateral muscles

 Brachioradialis

 Extensor carpi radialis longus

 Extensor carpi radialis brevis

 Extensor digitorum

 Extensor digiti minimi

 Extensor carpi ulnaris

 Anconeus

 Supinator

 Radial muscles

 Abductor pollicis longus

 Extensor pollicis longus

 Extensor pollicis brevis

 Extensor indicis

Hand Muscles

(All intrinsic hand muscles arise from anterior muscles of embryonic limb

and are innervated by the median and ulnar nerve from the anterior

divisions of the plexus)

 Thenar Muscles

 (All supplied by the median nerve except adductor pollicis)

 Abductor pollicis brevis

 Flexor pollicis brevis

 Opponens pollicis

 Adductor pollicis

 Hypothenar Muscles

 (All supplied by the ulnar nerve)

 Palmaris brevis

 Abductor digiti minimi

 Flexor digiti minimi

 Opponens digiti minimi

 Intermetacarpal Muscles

 (All supplied by the ulnar nerve except first two lumbricals)

 Lumbricales

 Palmar interossei

 Dorsal interossei

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Muscles of the upper limb

Anterior view

 1 Trapezius

 2 Deltoid

 3 Pectoralis major

 4 Biceps brachii

 5 Triceps brachii

 6 Serratus anterior

 7 Anterior antebrachial muscles

 8 Posterior antebrachial muscles

 9 Thenar muscles

10 Hypothenar muscles

 11 Temporalis

12 Masseter

13 Muscles of facial expression

14 Sternocleidomastoid

15 Cervical body wall muscles

16 Rectus abdominis

17 External oblique

18 Anterior thigh muscles

19 Medial thigh muscles

20 Linea alba

21 Tendinous intersection

22 Spermatic cord (cut)

23 Penis (cut)

24 Inguinal ligament

25 Umbilicus

26 Palmar aponeurosis

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