HUMAN ANATOMY – VOLUME 1

Fig. 95. Superficial muscles of thorax and abdomen.

1 — pectoralis major; 2 — axillary cavity; 3 — latissimus dorsi; 4 — serratus anterior; 5 — external oblique; 6 — aponeurosis of external oblique (of abdomen); 7 — anulus umbilicalis; 8 — linea alba (of abdomen); 9 — inguinal ligament; 10 — superficial inguinal ring; 11 — spermatic cord.

Fig. 96. Muscles of thorax and abdomen.

Pectoralis major muscle (on both sides) and external oblique muscle of abdomen(left) are removed. On the right side of a picture an anterior layer of rectus sheath is also removed.

1 — sternocleidomastoid; 2 — trapezium; 3 — pectoralis major (removed); 4 — pectoralis minor; 5 — serratus anterior; 6 — rectus abdominis; 7 — external oblique (of abdomen); 8 — umbilical ring; 9 — linea alba; 10 — aponeurosis of external oblique; 11 — pyramidalis; 12 — internal oblique (of abdomen); 13 — external oblique (cut off and partially removed); 14 — serratus anterior; 15 — pectoralis major; 16 — deltoid; 17 — subclavius.

upper extremities. This group includes the pectoralis major and pectoralis minor muscles, subclavius and serratus anterior muscles (Fig. 95 and 96). Beneath the superficial layer are the proper muscles of the thorax. They develop from the anterior portions of myotome. Both their origin and insertion are in the thorax.

The diaphragm can be discussed together with the muscles of the chest because of their close anatomical and functional association.

The pectoralis major muscle (m. pectorális májor) occupies a large area of the front thoracic wall. It has three parts, named according to their origin. The sternocostal part originates from the anterior surface of the sternum and cartilages of the upper 6 ribs. The clavicular part originates from the medial half of the clavicle; and the abdominal part—from the front of the rectus abdominis muscle sheath. Fascicles of the pectoralis major muscle converge laterally and insert into the crest of the greater tubercle of humerus.

F u n c t i o n: It lowers the raised arm, causes adduction and pronation. When the upper extremity is fixed (in a raised position), it raises the ribs and sternum, expanding the thoracic cavity and thus promoting inspiration.

I n n e r v a t i o n: medial and lateral pectoral nerves.

B l o o d s u p p l y: thoracoacromial artery, posterior intercostal arteries, anterior intercostal branches of the internal thoracic artery, lateral thoracic artery.

The pectoralis minor muscle (m. pectorális mínor) is flat, narrow, triangularly shaped. It is situated beneath the pectoralis major muscle. Its origin is on the anterior ends of ribs 3–5. It stretches laterally and upwards and is inserted into the coracoid process of the scapula.

F u n c t i o n: This muscle bends the scapula forward; when the shoulder girdle is fixed, it lifts the ribs.

I n n e r v a t i o n: medial and lateral pectoral nerves.

B l o o d s u p p l y: thoracoacromial artery, anterior intercostal branches.

The subclavius muscle (m. subclávius) is long and thin, and is situated between the clavicle and the first rib. It stretches laterally and attaches to the inferior surface of the acromial end of the clavicle.

F u n c t i o n: Moves the clavicle downwards and towards the front. I n n e r v a t i o n: subclavian nerve.

B l o o d s u p p l y: transverse cervical artery, throcoacromial artery.

The serratus anterior (m. serrátus antérior) is a flat muscle, situated on the anterolateral surface of the thorax. It originates from the upper 8–9 ribs by separate muscle fascicles, and inserts on the medial margin

and inferior angle of the scapula. Its upper and lower fascicles are oriented horizontally, the lower fascicles slanting upward and to the back.

F u n c t i o n: Shifts the scapula to the front and the side; lower fascicles turn its lateral angle medial and upwards. When the scapula is fixed this muscle lifts the ribs, thus expanding the thorax.

I n n e r v a t i o n: long thoracic nerve.

B l o o d s u p p l y: thoracodorsal artery, lateral thoracic artery, posterior intercostal arteries.

PROPER MUSCLES OF THE THORAX

The external intercostal muscles (mm. intercostáles extérni) are located in the intercostal spaces. They originate from lower edges of ribs, outside the costal grooves. Their fascicles stretch down and forward and insert into the upper border of the next rib.

F u n c t i o n: These muscles lift the ribs; in the back they strengthen the costovertebral joints.

I n n e r v a t i o n: intercostal nerves.

B l o o d s u p p l y: posterior intercostal arteries, musculophrenic artery, internal thoracic artery.

The internal intercostal muscles (mm. intercostáles intérni) are situated behind the external intercostals. They originate from the upper borders of ribs and insert into the lower borders of above-lying ribs. Their muscle fascicles take up the space from the sternum and costal cartilages of ribs 11 and 12 to the angles of ribs in the back. They are oriented obliquely, almost perpendicularly to the fascicles of the external intercostal muscles.

F u n c t i o n: lowering the ribs.

I n n e r v a t i o n: intercostal nerves.

B l o o d s u p p l y: posterior intercostal arteries, internal thoracic artery, musculophrenic artery.

The transversus thoracis muscle (m. transvérsus thóracis) lies on the internal surface of the anterior thoracic wall. It originates from the xiphoid process and lower half of the sternum. Its muscle fascicles diverge like a fan and insert into cartilages of ribs 2–11. The upper fascicles are oriented somewhat vertically, while the middle and lower fascicles are directed obliquely and horizontally.

F u n c t i o n: The muscle pulls down the costal cartilages and lowers the ribs.

I n n e r v a t i o n: intercostal nerves.

B l o o d s u p p l y: internal thoracic artery.

!

Muscles of the thorax are demonstrated in the table 9.

The subcostales muscles (mm. subcostales) are situated in the lower back portion of the internal surface of the thorax. They originate from the angles of ribs 10–12 and stretch upward and laterally. They span one or two ribs and inset into the internal surface of the above-lying rib.

F u n c t i o n: These muscles raise the ribs. I n n e r v a t i o n: intercostal nerves.

B l o o d s u p p l y: posterior intercostal arteries.

The diaphragm (diaphrágma, m. phrénicus) is a thin, wide musculotendinous septum, which separates the thoracic and abdominal cavities. The diaphragm is the main breathing muscle. It develops from cervical myotomes. Its convex side is turned upward, into the thoracic cavity, and its concave side looks into the abdominal cavity (Fig. 97).

Its muscle fascicles originate from the periphery and converging towards the center they form the central tendon of diaphragm (centrum tendineum). According to the origin, the diaphragm is divided into the lumbar, costal and sternal parts. The l u m b a r p a r t originates from the r i g h t and le f t c r u s e s from the medial and lateral arcuate ligaments and the anterior surface on lumbar vertebrae. The m e d i a l a r c u a t e l i g a m e n t (lig. arcuátum mediále) begins from the lateral surface of the L1 vertebra and attaches to the transverse process of the L2 vertebra. This ligament is stretched over the psoas major muscle. The l a t e r a l a r c u - a t e l i g a m e n t (lig. arcuátum laterále) stretches between the apex of L2 vertebra and rib 12. It is situated in front of the lumbar quadrate muscle. The two peduncles of the lumbar part of the diaphragm cross each other on the level of L1 vertebra, forming the a o r t i c h i a t u s (hiátus aórticus) that serves as a passage for the aorta and the thoracic duct. The edges of this opening are limited by fibrous lamina called the m i d d l e a r c u a t e l i g a m e n t, which protects the vessels, which pass through this opening from compression. Above and somewhat to the left of the aortic hiatus, in the lumbar part of the diaphragm, is the esophageal hiatus opening (hiátus oesophágeus), which is a passage for the esophagus and vagus nerve. Other vessels and nerves also pass between muscle fascicles of the lumbar part (the azygos and hemiazygos veins, the greater and lesser splanchnic nerves, the sympathetic trunk).

The c o s t a l p a r t of the diaphragm is formed by muscle fascicles, which originate from the internal surfaces of the lower six-seven ribs and insert into the centarl tendon of the diaphragm.

The s t e r n a l p a r t is the most narrow. It originates from the posterior surface of the sternum and converges into the central tendon.

There c e n t r a l t e n d o n has c a v a l o p e n i n g (forámen vénae cávae).

#

Fig. 97. Diaphragm and posterior abdominal muscles.

1 — central tendon; 2 — caval opening; 3 — oesophageal hiatus; 4 — medial arquate ligament; 5 — aortic hiatus; 6 — left crus of diaphragm; 7 -quadratus lumborum; 8 — psoas minor; 9 — psoas major; 10 — iliacus; 11 — iliac fascia; 12 — obturator externus; 13 — iliopsoas; 14 — right crus of diaphragm; 15 — lateral arquate ligament.

$

On top the diaphragm is covered by the endothoracic fascia and from below — by the endoabdominal fascia.

The diaphragm has weak places, in which muscle fibers are absent and the organs of the abdominal and thoracic cavities are separated only by the endoabdominal and endothoracic fasciae. These are the paired lumbocostal and sternocostal triangles. The l u m b o c o s t a l t r i a n g l e is situated between lumbar and costal parts of the diaphragm. The s t e r n o c o s t a l t r i - a n g l e is smaller and is situated between sternal and costal parts of the diaphragm. These triangles often become a site of diaphragmatic hernias.

F u n c t i o n: During contraction, the diaphragm flattens and drops down increasing the volume of the thorax. When the diaphragm contracts simultaneously with the muscles of the abdominal press, the intra-abdom- inal pressure increases.

I n n e r v a t i o n: phrenic nerve.

B l o o d s u p p l y: pericardiacophrenic artery, superior and inferior phrenic arteries, musculophrenic artery, posterior intercostal arteries.

FASCIAE OF THE THORAX

The s u p e r f i c i a l f a s c i a o f t h e c h e s t (f á s c i a s u p e r - f i c i á l i s) is weakly developed. The p e c t o r a l f a s c i a (f á s c i a p e c - t o r á l i s) has deep and superficial laminae. The s u p e r f i c i a l l a m i n a covers the pectoralis major muscle in the front. It attaches medially to the edge of the sternum; laterally it continues into the deltoid fascia; at the bottom it becomes the axillary fascia; and at the top it attaches to the clavicle. The d e e p l a m i n a of the pectoral fascia separates the pectoralis major and pectoralis minor muscle, forming a fascial sheath for the former. Laterally and at the bottom the deep lamina of pectoral fascia merges with the superficial lamina. Between the clavicle and the upper edge of the pectoralis minor the deep lamina has a thickening called the c l a v i p e c t o r a l f a s c i a (fascia clavipectoralis). Beneath this fascia are ribs and external intercostal muscles. The inside of the thorax is lined by the e n d o t h o r a c i c f a s c i a (f á s c i a e n d o t h o r á c i c a). It covers the internal intercostal muscles, transverse thoracic muscles, internal surfaces of ribs and the diaphragm.

TOPOGRAPHIC ANATOMY AND FATTY TISSUE SPACES OF THE

THORAX

The surface of the thorax has several palpable points of reference, including the jugular notch of the sternum, the clavicles, the xiphoid process of the sternum and the ribs. Jugular notch of the sternum corresponds

%

to the lower edge of the T2 vertebra. The sternal angle projects onto the intervertebral disc between T4 andT5 vertebrae. The lower edge of the body of the sternum is situated at the level of T10 vertebra. In men the contours of the pectoralis major and the d e l t o p e c t o r a l s u l c u s project onto the thoracic wall. In women the mammary gland is situated at the level of ribs 3–7. In very thin people a s e r r a t e d l i n e is visible along the side of the sternum, formed by fascicles of the serratus anterior and external oblique abdominal muscles. The skin of the chest is relatively thin. In men there is hair in the region of the sternum and scapulae. The skin contains many sebaceous and sweat glands in the area of the sternum, on the sides of the thorax and over the scapulae. The subcutaneous fat is moderately developed (more in the female). It contains superficial veins and arterial branches (from internal thoracic, intercostal, lateral thoracic arteries), as well as anterior and lateral branches of the intercostal nerves.

The superficial fascia, which is part of the superficial fascia of the body, forms part of the mammary gland capsule, giving off connective tissue septa, which divide the glands into lobes. Fascicles of the fascia extend from the capsule of the mammary gland to the clavicle. These are known as the s u s p e n s o r y l i g a m e n t s o f t h e b r e a s t (ligg. suspensória mammária).

Behind the pectoralis major and minor muscles there are three areas called the c l a v i p e c t o r a l, p e c t o r a l and s u b p e c t o r a l t r i a n - g l e s. The clavipectoral triangle is defined between the clavicle and the upper edge of the pectoralis minor (at the level of the clavipectoral fascia). Edges of the pectoralis minor muscle limit the pectoral triangle. The subpectoral triangle is defined between the lower edges of the pectoralis minor and pectoralis major muscles. In the region of the sternum the pectoral fascia accretes with its periosteum, forming a thick connective tissue lamina called the anterior sternal membrane.

Between the two pectoral muscles, which lie within fascial sheaths, is a subpectoral fatty tissue space. Beneath the pectoralis minor muscle is the deep fatty tissue space. Both of these are filled by fatty tissue. Between the internal and external intercostal muscles there is a thin layer of loose connective tissue, which contains vessels and nerves that pass along the costal grooves.

Questions for revision and examination

1.Name the muscles, which raise the ribs. What muscles lower the ribs?

2.Do the external and internal intercostal muscles take up the whole length of inter costal spaces? Describe the topographical differences between these two muscles.

3.Name the parts of the diaphragm and its openings.

&

4.Name the «weak» places in the diaphragm. Where are they situated and what forms their borders.

5.Name the fasciae and fatty tissue spaces of the chest and describe their topographic characteristics.

MUSCLES AND FASCIAE OF THE ABDOMEN

The abdomen (abdomen) is the region between the thorax and pelvis. Its upper border is drawn along the xiphoid process of the sternum, the costal arches and the T12 vertebra. Its lateral border passes from the costal arches, along the posterior axillary line down to the iliac crest. Its lower border is formed by anterior parts of the iliac crests and a provisory line that corresponds to the inguinal folds.

The abdominal muscles form the anterior, posterior and lateral walls of the abdominal cavity. According to their topography these muscles are divided into anterior, posterior and lateral.

Muscles of the anterior and lateral abdominal walls

This group of muscles includes the internal and external oblique muscles, transverse abdominal muscle, rectus abdominis and pyramidalis muscles. The oblique and transverse abdominal muscles are situated in layers, their muscular fibers oriented in different directions. The rectus abdominis and pyramidalis muscles are oriented longitudinally.

The external oblique muscle of the abdomen (m. oblíquus extérnus abdóminis) is situated superficially. It originates by muscle serrations on lateral surfaces on the lower 8th-9th ribs. The five upper serrations pass between serrations of the serratus anterior muscle, and the three lower ones — between serrations of the latissimus dorsi muscle. Its fascicles stretch down and medial, continuing into a wide flat aponeurosis. The upper and middle fascicles of the aponeurosis reach the anterior middle line, where they accrete with the aponeurosis of the opposite side, taking part in formation of the white line of the abdomen. The lower fascicles attach to the external lip of the iliac crest and the pubic tubercle, forming between them a thickened tendinous cord called the i n g u i n a l l i g a m e n t (l i g . i n g u i n á l e).

F u n c t i o n: During bilateral contraction this muscle lowers the ribs and bends the spine. During unilateral contraction it turns body to the opposite side. When the lower extremities are not fixed it lifts the pelvis forward. It is one of the muscles of the prelum abdominale muscles.

I n n e r v a t i o n: intercostal nerves (5–12), iliohypogastric nerve, ilioinguinal nerve.

B l o o d s u p p l y: posterior intercostal and lumbar arteries, lateral thoracic artery, superficial circumflex iliac artery.

'