Muscular system
1. Fibrous canals.
On the border with the bone, the fascia of the forearm forms on the opposite side a transverse thickening in the form of a ligament, which is called the retinaculum extensorum. This ligament, with the help of processes, fuses with the opposite surface of the radius and ulna. Between these processes, under the ligament there are 6: some bone-fibrous, some only fibrous canals, through which the tendons of the extensors of the fingers and the bone pass.
In the first canal, the tendons of m/ abductor pollicis longug and m. Extensor pollicig brerig pass. In the second, the tendons of mm. Extengoreg carpi radialeg londuf et brevig. In the third, which crosses the previous one obliquely, the tendon of m. Extensor pollicis longuf; in the fourth, the tendon of m. Extensor indicis; in the fifth, located more superficially, the tendon of m. Extensor digiti minimi and, ending in the sixth tendon m. extensor capri wnaris. The walls of the channels are lined with a synovial membrane, which above and below the retinaculum extensorum twists on the tendon and covers them, forming tendon sheaths of the opposite muscles. The number of sheaths is equal to the number of channels.
There are 4 fibrous channels of the lower extremities. The most lateral and widest channel, which is located under the very beginning of the retinaculum mm. extensorum, snferiurs, passes the tendons of m. digitorum longus and m. peroneug terting. The next channel passes the tendons of m. extensor hallucis longuf, and the third, most medial - the tendon of m. tibialig aherior. The tendons pass through the channels, surrounded by synovial sheaths. The fourth channel, which lies after the middle, ends with vascular nerves.
2. Palmar aponeurosis.
On the palmar surface of the fascia in the middle of the palm is significantly thickened and forms a strong palmar aponeurosis there, which is a continuation of the tendon. The palmar aponeurosis has the shape of a triangle, the apex of which lies on the retinaculum flexorum, and the base is directed towards the fingers, where the aponeurosis diverges into four flat bundles, between which transverse fibers extend. Under the aponeurosis lies a flat fibrous ligament that holds the flexor tendons and is therefore called the retinaculum flexorum. On both sides of the palmar aponeurosis, where it passes into thin plates, dressing thenar and hypothenar, fascial sheets depart from it in depth, which grow together with the deep fascia of the palm. So in the middle part of the palm there is a container in which the flexor tendons lie, and mm. lumbricales. In addition to the deep fascia of the palm, there is also a fascia that covers the interosseous muscles on the opposite side of the hand, fused with the periosteum of the bones of the belt.
3. Synovial sheaths.
In the area of the radiocarpal joint, 3 channels enter.
The ulnar nerves and vessels pass through the cubital canal. In the canalis capri radialis lies the flexor capri radialas tendon surrounded by synovial sheaths. In the canalis carpalis there are 2 sections of the synovial sheath: 1) for the tendon of mm. flexores digitorum superficialis et profurdus and 2) for the tendon of m. flexoris pollicis longus. The first is a medially located voluminous bag that captures 8 tendons of the deep and superficial flexors of the fingers. From above it protrudes 1-2 cm proximal to the retinaculum flexorum, and from below it reaches the middle of the palm. Only on the side of the little finger does it continue along the tendons that bend its long muscles, surrounding them and reaching with them the base of the distal phalanx of the 5th finger.
The second sheath is located laterally, is a long and narrow channel in which the tendon of the long flexor of the thumb is fixed. From above it also protrudes 1-2 cm proximally, and from below it continues along the tendons to the base of the lister phalanx of the first finger. The remaining 3 fingers have separate sheaths that capture the flexor tendons of the corresponding finger. These sheaths extend from the line of the metacarpophalangeal joints to the base of the carpal phalanges. This means that the II-IV fingers on the palmar side have isolated sheaths for the tendons of their common flexors, in the section of the corresponding distal half of the metacarpal bones, they are completely devoid of them.
4. Axillary fossa.
The axillary fossa, in the formation of which the muscles of the upper limb participate, has four walls and two openings.
The anterior wall is formed by the pectoralis major and minor muscles; posterior – by the infraspinatus and teres major muscles and the latissimus dorsi muscle; medial – by the serratus anterior muscle, and lateral – by the humerus and shoulder muscles.
The upper opening of the axillary fossa is limited by the I rib, the clavicle with the subclavian muscle and the upper edge of the scapula. Large vessels and nerves pass through it from the side of the neck. The lower opening of the axillary fossa is limited in front by the lower edge of the pectoralis major muscle, behind – by the lower edge of the latissimus dorsi muscle, medially – by the serratus anterior muscle and externally – by the humerus with the shoulder muscles. The axillary fossa is filled with fatty tissue, in which lymph nodes of various sizes are located.
The ulnar fossa.
In the anterior area there is an ulnar fossa, bounded above by the longus and brachialis muscles, outside by the brachioradialis, and inside by the teres muscle – adductor. Within the fossa, directly under the skin, the median vein of the elbow is located, and in its depth lie the brachial artery and veins, as well as the median nerve.
In the lower part of the anterior surface of the forearm, three grooves are defined between the tendons of the flexor muscles. The radial groove is bounded outside by the tendon of the brachioradialis muscle, and inside by the tendon of the radial muscle – flexor of the wrist. In the depth of the groove lies the radial artery, its pulsation is usually palpated here. In addition, the radial veins and the superficial branch of the radial nerve are located here. The median groove is formed outwardly by the tendon of the radial muscle - the flexor of the wrist and inwardly by the tendon of the superficial muscle - the flexor of the fingers. The median nerve is located in this groove. The ulnar groove is limited outwardly by the tendon of the superficial muscle - the flexor of the fingers and the ulnar muscle - the flexor of the wrist. The ulnar artery, veins and nerves pass through this groove.
The fascial membranes, together with the bones of the forearm, form the anterior, posterior and lateral sheaths.