Anterior Brachial Muscles

The muscles of the anterior antebrachium form three

distinct muscle layers. The superficial group has four superfi cial muscles (pronator teres, fl exor carpi radialis, palmaris longus, and fl exor carpi ulnaris) covering the intermediate fl exor digitorum superfi cialis. All fi ve of these muscles share a common attachment on the medial epicondyle of the humerus. The three deep muscles (fl exor digitorum profundus, fl exor pollicis longus, and pronator quadratus) do not cross the elbow joint. Other than the two pronators, all the muscles are fl exors of either the wrist or digits. The median nerve innervates all but the fl exor carpi ulnaris and the ulnar half of the fl exor digitorum profundus, both of which are supplied by the ulnar nerve.

Superficial muscles of the right antebrachium

Anterior view, hand pronated

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189

There are two muscle groups in the posterior

antebrachium — the eight muscles of the lateral group that share a common attachment on or near the lateral epicondyle of the humerus and the four muscles of the radial group that course along the distal aspect of the radius to insert on the thumb and fi rst fi nger. Like the triceps of the posterior brachial compartment, all the muscles of the posterior antebrachium receive innervation via the radial nerve. With a few exceptions, the muscles are extensors of either the elbow, wrist, or digits.

Superficial muscles of the right antebrachium

Posterior view, hand pronated

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11

11

Muscles of the thenar eminence

5

Muscles of the hypothenar eminence

17

10 10

12

18

11

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12 Lower Limb Muscles

The design of the inferior limb musculature is similar to that of the true limb muscles of the superior limb. The major difference between the two limbs is that the proximal end of the lower limb forms a direct skeletal attachment to the vertebral column via the strong sacro-iliac joint, unlike the unattached scapula of the superior limb. Because of this difference, the inferior limb does not require body wall muscles to support, stabilize, and suspend it from the axial skeleton. There are two additional features that are important to keep in mind when studying this powerful locomotor limb. First, during development of the lower limb the embryonic posterior muscles rotate and reposition themselves to the anterior aspect of the limb. For this reason the knee and ankle move directly opposite the elbow and wrist. The second notable feature is that there are three muscle compartments in the thigh and leg, as compared

to just two in the brachium and antebrachium. One of the two original compartments in each lower limb segment (thigh and leg) splits to give rise to an additional compartment. The thigh has an anterior compartment and a posterior compartment, but the posterior compartment is subdivided into posterior and medial compartments. The leg has a large posterior compartment and a smaller anterior compartment and the anterior compartment is subdivided into anterior and lateral compartments. As with the upper limb, we present the muscles of the lower limb proper in their muscle compartments. Again, this greatly simplifies the learning process because most of the muscles in a compartment share simi-

lar attachments, perform common actions, and have a common nerve supply. Unlike the compartmental muscles of the lower limb proper, the proximal muscles of the lower limb that surround the hip joint are a more diverse group of muscles. Some are true limb muscles, while others are annexed muscles from the trunk wall. We organize these hip muscles into three groups — the deep hip rotator muscles, the gluteal muscles, and the hip flexors.

Find more information about the muscles of the lower limb in

R E A L A N AT O M Y

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The muscles of the lower limb share similarities with their upper limb counterparts, yet have important differences. As you will notice in the groups below there are no homologues in

the lower limb to the scapular muscles of the upper limb. Like the shoulder muscles, the muscles surrounding the hip joint are a varied group of muscles, with some annexed from the body wall of the abdominopelvic region. In the limb proper the muscles develop in muscular compartments as they do in the upper limb; however, the embryonic posterior aspect of the limb rotates to an anterior position. As a result, the nerves that arise from the posterior divisions of the lumbosacral plexus innervate the anterior muscle compartments, and the nerves from the anterior divisions of the plexus innervate the posterior muscle compartments. The developmental groups of muscles and their nerve supply are outlined below.

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21 24

16

17

18

25

3

23

6

4

Deep muscles of the thigh

Anterior view

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The six muscles of the medial compartment are all capable of adducting the hip joint. The pectineus and four adductor muscles all originate from a medial position on the pubis

and ischium and project laterally to insert on the posterior surface of the femur. The gracilis muscle differs from the others in the group by crossing the knee joint in addition to the hip. It courses with the sartorius muscle as a fl exor of the knee. With the exception of the pectineus and condylar part of the adductor magnus, all the muscles are innervated by the obturator nerve, which arises from the anterior divisions of the lumbar plexus.