In all expulsive acts, as sneezing, laughing, crying, coughing, and in the act of defecation, urination, and expulsion of the fetus during delivery, it assists the abdominal muscle to raise the intra-abdominal pressure. The action of the diaphragm can be seen in patients under ether, when the upper portion of the abdomen will demonstrate the gradual and steady ascent and descent of the diaphragm under forced or abdominal breathing. The Fasciae and Muscles of the Abdomen The fascia of the abdomen is divided into a superficial and deep portion. The superficial fascia is continuous above with the fascia of the thorax and back, below with that of the thigh. Its lower fourth on the abdomen divides into a superficial layer — called Camper's fascia, and a deep layer — termed Scarpa's. The deep layer is attached to Poupart's ligament, and is continued around the male and female genitalia; the superficial layer also passes to the male and female genitalia. The deep fascia of the abdomen is so adherent to the underlying structures that it is difficult to see. The Muscles of the Abdomen. — They are as follows: External oblique. Transversalis. Internal oblique. Rectus. Pyramidalis. The external and internal oblique and the transversalis are thin, flat, broad muscles which possess aponeuroses and they all form with the rectus the anterior and lateral abdominal walls, being lined — the transversalis — by the peritoneum. They are arranged one on either side. The aponeuroses of the oblique and transversalis pass toward the outer edge of the rectus and ensheath the two halves. In a general way the oblique and transversalis muscles are attached to the lower ribs, crest of the ilium, and Poupart's ligament. The Fasciae and Muscles of the Thoracic Region, Fascia, of Pectoral Region (Chest). — Superficial contains the mammary gland, sending septa into it and supporting it. The deep fascia is thin, covering the surface of the pectoralis major muscle; it is attached to the middle of the front of the sternum, above to the clavicle, and below is continuous with the fascia over the shoulder, axilla, and thorax. It encloses the space between the pectoralis major and latissimus dorsi muscles; it is called in this region the axillary fascia. The Muscles of the Anterior Thoracic Region. These are as follows: Pectoralis major. Subclavius. Pectoralis minor. Pedoralis Major. — This arises from the inner half of the anterior surface of the clavicle, the sternum, from the upper six rib cartilages and from the anterior sheath of the rectus and external oblique aponeurosis. The fibers converge to be inserted by two tendons, united along the lower margin, into the external bicipital ridge of the humerus. Subclavius. — This arises from the groove on the under surface of the clavicle and recess between the conoid and trapezoid ligaments: inserted into the junction of the first rib with its cartilage between the fibers of the costoclavicular ligament. Pedoralis Minor. — This arises from three ribs near their cartilages, usually the third, fourth, and fifth, often the second, third, and fourth or fifth, and from the intercostal aponeurosis; insertion, inner border and upper surface of the coracoid process of the scapula; a bursa is under its insertion. The linea alba is a narrow depression seen along the middle line of the abdomen, extending from the tip of the breast bone — ensiform — to the symphysis pubes. It is formed by the union of the aponeuroses of the oblique and transversalis muscles, which surround the recti muscles and adhere to the fascia and skin. A little below the midpoint of the hnea alba is a scar — the result of the healed umbilical cord, called the umbilicus (navel). The linea semilunaris is a depression seen on the outer side of each rectus abdominis muscle, and corresponds to the line of fusion of the aponeuroses of the oblique and transversalis muscles, as they blend to pass in front and behind the recti muscles to form the sheath of the latter muscles. It extends from opposite the ninth costal cartilage to the spine of the pubic bone. Linese transversse are depressions seen along the recti muscles, and correspond to the attachment of the aponeuroses of the abdominal muscles to the rectus. They are usually three — one below the ensiform cartilage, one between the ensiform and the umbilicus, and one opposite or below the umbilicus. Actions of the Abdominal Muscles. — When the thorax and pelvis are fixed these muscles acting together constrict the abdominal cavity, and raising the intra-abdominal pressure — also assisted by the diaphragm — aid in expelling the fetus from the uterus, feces from the rectum, urine from the bladder. The Posterior Muscles of Abdomen (Hiac Region) The iliac fascia covers the iliopsoas muscle, within the back part of the abdominal cavity stretched from the iliac crest to the iliac portion of the iliopectineal line. Below it passes beneath the femoral vessels, forming the hinder part of the femoral sheath; outside the vessels it unites with the transversalis fascia at Poupart's ligament. Quadratus Lumbonim. — A quadrilateral muscle placed between the last rib and the pelvis. Origin, iliolumbar ligament, external lip of the crest of the ilium for two inches, from two, three, or four lumbar transverse processes by fleshy slips passing up anteriorly; insertion, inner half of last rib and upper four lumbar transverse processes. Nerves. — Last dorsal and upper lumbar. Actions. — Lateral flexion of both may extend the spine. Draws down the last rib, giving fixed point for the diaphragm, and aids inspiration. Fixed above, draws pelvis to one side, or both draw it forward. Iliopsoas. — It has a broad outer head, iliacus, and a narrow inner head, psoas magnus. Iliacus. — Origin, upper half of the iliac fossa down as far as the anterior inferior spine, posteriorly from ala of the sacroiliac and iliolumbar ligaments. Inserted mostly into tendon of the psoas; outermost fibers pass to the femur in front of and below the small trochanter. Psoas Magnus (or Major). — Origin, by fleshy slips from anterior surfaces and lower borders of the lumbar transverse process, and by a series of processes, each from a disk and contiguous margins of two bodies; the highest is attached to the last thoracic and first lumbar, and lowest to the fourth and fifth lumbar and intervertebral substance between them; fibers also come from the sacroiliac joint and sacrum. These attachments are connected with arches passing over the middle of the vertebrae. The fibers all unite to a thick, long muscle running along the brim of the pelvis, passing under Poupart's ligament, and inserted by a tendon into the small trochanter; separated by a bursa. The common tendon is also separated from the capsule of the hip by a bursa. Psoas Parvus (or Minor). — Placed on the surface of the psoas magnus; rises from the bodies of the last thoracic and first lumbar vertebrse and disk between; ends in a flat tendon merged into the iliac fascia and inserted into the iliopectineal line and eminence. When present its origin is variable; was absent on both sides in 40 per cent, of cases. The Muscles and Fasciae of the Perineum These are the structures which enclose the space between the rami of the pubes and ischii on both sides and the pubic arch and subpubic ligament in front, while they are bounded behind by a line extending transversely between the anterior edge of the tuberosities of the ischii on both sides. The space in front of this line is termed the perineum, and behind the line, the space in front of the coccyx, is called the ischiorectal region; this space is bounded on the sides by the gluteus maximus muscles. The perineum can be demonstrated only by having the subject on its back with the limbs flexed on the abdomen. The structures to be seen are the anus (outlet of rectum), the scrotum in the male, and the vagina in the female. The perineum is covered by skin, superficial fascia divisible into a superficial layer, and a deep layer — called Colics'. The deep perineal or subpubic fascia or triangular ligament of the urethra is stretched across the subpubic arch and consists of two layers; the inferior layer extends back to the central point of the perineum, attached to the ischiopubic rami, connected at its base with the other layer, and continuous with the recurved margin of the superficial perineal fascia. The superior (deep) layer consists of right and left lateral halves, separated in the middle line by the urethra close to the prostate, and continuous on each side with the fascia covering the obturator internus muscle. The levator ani muscle is between this layer and the rectovesical fascia. MUSCLES AND FASCIA OF UPPER EXTREMITY 148 Muscles and Fasciae of the Shoulder The Acromial Region.— The deep fascia is strong and tendinous over the back of the deltoid and infra-spinatus; the infraspinatus fascia covers the teres minor and splits at the posterior border of the deltoid, a deep layer passing to the shoulder-joint under that muscle, a superficial layer to the spine of the scapula over the muscle. Deltoid. — Origin in three portions : an anterior from the front of the outer third of the clavicle, a middle from the point and outer edge of the acromion, a posterior from the lower border of the scapular spine and triangular surface at its inner end, and from the infra-spinatus fascia. These converge into the tendon of insertion into the deltoid tubercle of the humerus. The Posterior Scapular Region. — The muscles of this region are as follows : Supraspinatus. Teres major. Infraspinatus. Teres minor. Supraspinatus. — This arises from inner part of the supraspinous fossa to region of the notch, from supra-spinous fascia and transverse ligament; adherent to capsule and infraspinatus tendon; inserted into the upper of the three facets on the great tuberosity of the humerus. Infraspinatus. — It arises from the inner two-thirds of the infraspinous fossa, and under surface of the spine of the scapula, the fibers converge to a tendon concealed within the muscle and inserted into the middle facet of the great tuberosity. It may be inseparably connected with the teres minor. Teres Minor. — Origin, from narrow grooved surface on the back of the scapula close to the axillary border, from septa between it, the teres major, and infra-spinatus; inserted into the lowest facet on the great tuberosity and into the shaft for a short distance below. Teres Major. — Is a thick somewhat flattened muscle. Origin, from the oval surface on the back part of the inferior angle of the scapula, and the fibrous septa common to it, and the teres minor and infraspinatus; inserted, by a flat tendon into the inner ridge of the bicipital groove of the humerus. The Anterior Scapular Region. — Subscapularis. — Origin, by muscular and tendinous fibers from the venter of the scapula and groove along the axillary border, insertion, small tuberosity of the humerus and into the shaft for a short distance. As in the deltoid, this muscle contains two sets of septa — one from the origin, and one from the insertion for attachment of the oblique muscular fibers. Some fibers from the axillary border of the muscle are usually inserted into the capsule, known as the subscapularis minor. The Muscles and Fasciae of the Arm The aponeurosis of the arm (deep fascia) is thin over the biceps, strong over the triceps, and is attached to the humerus, intermuscular septa. The Muscles of the Anterior Humeral Region. — The muscles of this region are: Biceps. Coracobrachialis. Brachialis anticus. Biceps. — Its short or inner head arises with the coracobrachialis from the tip of the coracoid process; the long head, from the upper end of the glenoid cavity; within the capsule by a tendon continuous on each side with the glenoid ligament; these two heads form a belly in the middle and lower part of the arm. The tendon of insertion is slightly twisted and attached to the back part of the tuberosity of the radius, separated from the forepart by a bursa. From the inner side of the tendon a part branches off as an aponeurotic band or semilunar fascia, and blends with the deep fascia of the forearm stretched across the brachial vessels and median nerve. Coracobrachialis. — Origin, tip of the coracoid between the pectoralis minor and short head of the biceps; insertion, inner border and inner surface of the humerus near its middle, between the triceps and the brachialis anticus. Brachialis anticus. — Arises from the lower half of the front of the humerus, nearly the whole of the internal intermuscular septum, and upper part of the external. It is adherent to the capsule of the elbow-joint, and often sends a slip into it, and is inserted into the inner part of the rough surface at the junction of the coronoid process with the shaft of the humerus. The Muscles of the Posterior Humeral Region. — The muscles of this region are: Triceps. Subanconeus. Triceps occupies the entire posterior aspect of the humerus. Three heads are inserted into a common tendon occupying the posterior surface of the muscle from the middle of the arm to the elbow. The middle or long head arises from the inferior glenoid tubercle of the scapula and adjacent portion of the axillary border; this forms the middle and superficial part of the muscle and ends on the inner margin of the tendon. The external head arises above the spiral groove and from an aponeurotic arch of the external intermuscular septum as it crosses it, extending to the teres minor insertion above, and inserted into the upper end and outer border of the tendon. The internal or deep head arises from the whole posterior surface of the humerus below the spiral groove, from the lower part of the external intermuscular septum, from the whole of the internal, as high as the teres major; some of its fibers are inserted directly into the olecranon process of the ulna, but most join the deep surface of the tendon. The common tendon is inserted into the tuberosity of the olecranon process of the ulna, and externally a band is prolonged over the anconeus to the fascia of the forearm and posterior border of the ulna; it may send a slip to the capsule. Muscles and Fasciae of the Forearm The superficial fascia is most distinct at the elbow, contains the superficial veins, and below connects the skin with the palmar fascia. The aponeurosis of the forearm (deep fascia) is composed largely of transverse fibers, strengthened by expansions from the condyles of the humerus, olecranon, and fascia over the biceps and triceps. It sends in a thin layer between the superficial and deep muscles; this anterior portion of the fascia forms at the wrist the anterior annular ligament, which binds down the tendons of the flexor muscles. The posterior portion sends off septa between the muscles and forms the posterior annular ligament, which firmly holds in position the tendons of the extensor muscles. The tendon of the palmaris longus muscle is the only one passing in front of the anterior annular ligament.
Key Takeaways
- Abdominal muscles assist in expelling waste and aiding childbirth by raising intra-abdominal pressure.
- The linea alba is a key anatomical landmark formed by the union of abdominal muscle aponeuroses.
- Psoas magnus plays a crucial role in lateral flexion and supporting the diaphragm.
Practical Tips
- Understanding the anatomy of the abdomen can help in assessing injuries or conditions that affect these muscles, such as hernias or postpartum recovery.
- Knowing the functions of different abdominal muscles is essential for effective physical therapy and rehabilitation exercises.
- The knowledge of muscle attachments and actions can aid in diagnosing and treating musculoskeletal issues.
Warnings & Risks
- Improper handling of the abdomen, such as excessive force during childbirth or surgery, can lead to complications like hernias.
- Ignoring pain or discomfort in the abdominal region may mask more serious underlying conditions that require medical attention.
- Incorrect posture and movement patterns can strain abdominal muscles, leading to chronic pain and reduced functionality.
Modern Application
While the historical techniques described in this chapter provide foundational knowledge for understanding muscle function, modern medicine has refined diagnostic tools and treatment methods. However, the basic principles of muscle anatomy and their functions remain crucial for emergency response, physical therapy, and general health maintenance.
Frequently Asked Questions
Q: What is the linea alba, and why is it important?
The linea alba is a narrow depression along the middle line of the abdomen that forms from the union of abdominal muscle aponeuroses. It's important because it helps in assessing conditions like hernias or postpartum recovery where these muscles might be compromised.
Q: How do the psoas muscles contribute to breathing and movement?
The psoas muscles, particularly the psoas magnus, play a role in lateral flexion of the spine and aid inspiration by providing a fixed point for the diaphragm. They also help draw the pelvis forward or to one side.
Q: What are the functions of the abdominal muscles during childbirth?
During childbirth, the abdominal muscles work together with the diaphragm to raise intra-abdominal pressure, assisting in expelling the fetus from the uterus. This is a critical function that helps manage the force required for delivery.