HUMAN ANATOMY – VOLUME 1

point of insertion of the muscle is shifted up to ribs 2–4. Occasionally, this muscle was found absent on one or, more rarely, both sides.

The pyramidalis muscle is often underdeveloped. In 25 percent of cases it is absent.

Muscles of facial expression

Occipitofrontalis muscle. Sometimes there is also a transverse occipital muscle, stretching from the occipital crest to the mastoid process of the temporal bone.

The temporoparietalis muscle is often absent.

The procerus muscle is sometimes absent.

Orbicularis oculi muscle. The absence of one of its parts is possible. There have been cases of enlargement of its orbital part.

The corrugator supercilii muscle is often absent or underdeveloped. The nasalis muscle is in some rare cases absent.

The depressor septi nasi muscle is not consistently met.

The levator labii superioris muscle may be united with one of its neighboring muscles. It may also split into two or three muscles.

The orbicularis oris muscle is sometimes fused with adjacent muscles.

The zygomaticus major muscle is sometimes absent.

The zygomaticus minor muscle is inconstant. The point of origin of this muscle is sometimes shifted.

Risorius muscle. This muscle is often absent on one or both sides. Often it fuses with the minor zygomatic muscle.

Buccinator muscle. It may have accessory fascicles. The muscle may be split into two layers.

The depressor anguli oris muscle is sometimes absent.

The depressor labii inferioris muscle sometimes fuses with the adjacent muscles. It may also be absent.

The mentalis muscle is often absent, and sometimes is split into two parts.

Anterior, superior and posterior auricularis muscles. Sometimes one or all of these muscles are absent. There have been cases of fusion of these muscles into one.

Muscles of mastication

The temporal muscle sometimes gives off fascicles towards the other masticatory muscles

The masseter muscle sometimes has additional fascicles.

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The medial pterygoid muscles may have additional fascicles. The lateral pterygoid muscle may have a common origin with the

medial pterygoid muscle. Sometimes one of its head is absent. The superior head may be fused with the temporal muscle.

Muscles of the neck

Platysma muscle. There had been cases when this muscle is partially or completely absent. It may have additional fascicles.

Sternocleidomastoid muscle. The number of its heads varies between 2 and 4. The muscle may be partially or completely absent. Occasionally, there is an accessory cleidomastoid muscle, which is inserted into the superior nuchal line.

The digastric muscle may have accessory fascicles, which connect its venters with neighboring muscles. Sometimes one of its venters is absent.

The stylohyoid muscle may be completely or partially split, or may have accessory fascicles.

Geniohyoid muscle. There have been cases of doubling of this muscle. Sometimes it is absent. It may also have accessory fascicles connecting it to neighboring muscles.

Sternohyoid muscle. This muscle has also been described to double. It may have accessory fascicles, and is sometimes absent. It may be split into a cleidohyoid and sternohyoid muscles.

Sternothyroid muscle. The point of origin of this muscle may vary (ribs 1 and 2).

The omohyoid muscle may lack the intermediate tendon. The number of its venters may increase to 3–5.

The thyrohyoid muscle is occasionally absent. It may be split into two parts, which have separate origins.

The anterior scalene muscle is, in some cases, absent, split into two parts, or united with the middle scalene muscle.

The middle scalene muscle is sometimes absent. It may be split, or its dorsal part may develop as a separate lateral scalene muscle.

The posterior scalene muscle may be absent. Its point of insertion may vary between ribs 3–5. It has been described in some cases to unite with the middle scalene muscle.

The longus colli muscle is sometimes absent. It may completely or partially fuse with the long muscle of the head.

The longus colli muscle is occasionally united with the long muscle of neck. It may be absent of split longitudinally into two parts.

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The rectus capitis anterior and rectus capitis lateralis may be absent on one or both sides (in rare cases).

Muscles of the upper extremity

The deltoid muscle. Sometimes a part of this muscle is absent or underdeveloped. Its clavicular part may be a separate muscle. Fusion with the adjacent muscles is also possible.

The supraspinatus muscle is sometimes absent or underdeveloped.

The infraspinatus muscle may vary in size.

The teres minor muscle is sometimes absent. There have been cases of its fusion with the infraspinous muscle, and of separation of an inferior fascicle, which is inserted into the greater tubercle of the humerus.

The teres major muscle is occasionally absent. It may fuse with the tendon of the latissimus dorsi muscle or the tendon of the long head of the triceps.

The subscapularis muscle may split into several fascicles, which have different places of insertion (capsule of the shoulder joint, coracoid process, etc.).

The coracobrachialis muscle is sometimes absent. It may be split, or may have 2–3 accessory fascicles.

The biceps brachii muscle. One of the heads of this muscle may be absent. In very rare cases the whole muscle may be absent. The number of heads may increase to 3–5.

The brachialis muscle sometimes has two heads of origin, attached on either side of the deltoid tuberosity. This muscle sometimes unites with adjacent muscles.

The triceps brachii muscle rarely develops with anomalies. It has been recorded to divide into two parts. It may fuse with the infraspinous, the teres major or the anconeus muscle.

The anconeus muscle is sometimes absent.

The brachioradialis muscle sometimes originates from the deltoid tuberosity. It may be split along its whole length.

The pronator teres muscle is occasionally absent. The number of its heads may increase up to 3–4.

The flexor carpi radialis muscle may unite with the adjacent muscles, or may be divided longitudinally into two parts.

The palmaris longus muscle is absent in 25 percent of cases. It is sometimes split into two muscles. The relationship between the lengths of its venter and tendon may vary, as well as the points of insertion and origin, and the thickness of the muscle.

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The flexor carpi ulnaris may lack its ulnar part. It may unite with neighboring muscles (the palmaris longus muscle, etc.).

The flexor digitorum superficialis may lack its radial head or a tendon of one of the digits. Sometimes its tendons are inserted into the radial edge of the middle phalanx.

The flexor digitorum profundus may be missing a tendon of one of the digits. It may fuse with adjacent muscles.

The flexor pollicis longus is occasionally absent. It may have an additional fascicle, which stretches from the coronoid process of ulna.

The extensor carpi radialis longus may have up to 3–5 heads. Sometimes it is absent or is united with the adjacent muscles.

The extensor carpi radialis brevis may be fused with the extensor carpi radialis longus. This muscle is sometimes doubles and occasionally absent. It sometimes is inserted into the IV metacarpal bone.

The extensor digitorum may be divided into several separate muscles. There have been cases with an additional tendon stretching to the first digit, and lack of a tendon of the fifth digit.

The extensor digiti minimi is occasionally absent.

The extensor carpi ulnaris is sometimes doubled or fused with the neighboring muscles. It may have an additional tendon, which attaches to the capsule of the V metacarpophalangeal joint.

The supinator muscle sometimes divided into superficial and deep layers. On rare occasions this muscle is replaced by fibrous fascicles.

The abductor pollicis longus often unites with the short extensor of thumb. Sometimes it is partially of completely split. It may have an additional tendon, which stretches to the first metacarpal bone.

The extensor pollicis brevis may be partially or totally split. Part of its tendon fascicles may attach to the distal phalanx of thumb.

The extensor pollicis longus is occasionally absent. This muscle may be doubled, and may have an additional tendon, stretching towards the phalanges of the second digit. Its venter may fuse with the extensor muscle of index finger, or with the short extensor or long abductor muscle of thumb.

The extensor indicis is sometimes doubled. It may have an additional tendon, directed to the first finger. Sometimes this muscle is united with neighboring muscles.

The abductor pollicis brevis may fuse with adjacent muscles. The flexor pollicis brevis may be underdeveloped, or may lack one

of its head. Its deep head sometimes fuses with the opposer muscle of thumb.

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The opponens pollicis may be united with adjacent muscles. Sometimes this muscle is absent.

In the adductor pollicis the transverse head sometimes develops as a separate muscle. There may also be additional fascicles, which are inserted into the II–III metacarpal bones.

The palmaris brevis muscle may originate from the triquetral or pisiform bones. This muscle may be absent.

The abductor digiti minimi muscle is occasionally absent. It may be doubled, or it can have additional heads of origin on the neighboring muscles.

The flexor digiti minimi brevis is occasionally absent. It may fuse with neighboring muscles, or may have an additional tendon.

The lumbrical and interosseeous muscles. One or several of these muscles may be doubled, or may be absent.

Muscles of the lower extremities

The iliopsoas muscle. The level of fusion between the iliac and major psoas muscles is variable.

The psoas minor muscle is inconstant. Sometimes this muscle is doubled.

The piriformis muscle may be absent, or may be divided into 2–3 parts.

The gluteus maximus muscle may be united with the gluteus medius or with the tensor muscle of fascia lata.

The gluteus medius and minimus muscles may be united with the piriform muscle or the tensor muscle of fascia lata. There is sometimes additional (fourth) gluteal muscle, which is inserted into the capsule of the coxal joint.

The tensor of fascia lata muscle may be absent or, occasionally, doubled.

Superior and inferior gemellus muscles. One or both of these muscles may be absent.

The quadriceps femoris muscle may have up to 5–6 heads of origin, or may lack one of its heads.

The biceps femoris muscle may have up to 3–4 heads. In some cases its short head may be missing.

The semimembranosus muscle is occasionally absent. Sometimes it has accessory fascicles, which form a tensor muscle of the crural fascia.

The semitendinosus muscle is occasionally absent, or may be doubled.

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The gracilis muscle is sometimes absent.

The pectineus muscle may be absent. It may insert on the greater trochanter of the femur.

Thet adductor brevis muscle may be absent, or may be divided into two venters by an intermediate tendon.

The adductor magnus muscle sometimes fuses with the adductor longus and brevis muscles, the lumbar quadrate muscle, or the semimembranosus muscle.

The triceps surae muscle may lack one of its heads, or may have additional heads, which originate from the popliteal surface of femur.

The popliteus muscle is sometimes absent.

The flexor digitorum longus may also occasionally be absent. The tibialis anterior muscle may be doubles or may be absent. It

may be inserted into the II–IV metatarsal bones.

The extensor hallucis longus muscle may be absent (very rare). The peorneus longus muscle is sometimes absent. This muscle

may be inserted into the on bases of the III–V metatarsal bones.

The peroneus brevis muscle may have an accessory fascicle, which is inserted into the dorsal surface of the fifth toe.

The extensor digitorum brevis muscle may be absent. The extensor hallucis brevis muscle is occasionally absent.

The adductor hallucis is often split into two parts, which have their own tendons. It may also have an additional tendon, which is inserted into the proximal phalanx of the second toe.

The flexor hallucis brevis muscle, as all the other plantar muscles of the foot, may be absent or may unite with adjacent muscles.

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SPLANCHNOLOGY

(THE STUDY OF INTERNAL ORGANS)

Internal organs are situated in regions of the head and neck, and in the thoracic, abdominal and pelvic cavities. They take part in metabolic functions of the organism, providing it with nutrients and eliminating the byproducts of metabolism.

According to their development, topographic characteristics, anatomy and functions internal organs are grouped into several organ systems and apparatuses. These include the digestive and respiratory systems, and the urogenital apparatus, which consists of the urinary and reproductive systems. The organs of the digestive system are located in the regions of the head, neck, thorax, abdomen and pelvis. The respiratory organs are situated within the neck and thorax, and the urogenital organs lie in the abdominal and pelvic cavities. Situated inside the thorax, next to the respiratory and digestive organs, is the heart — a vital organ of the cardiovascular system. The abdominal cavity contains the spleen, which is an organ of the immune system. Special significance is given to endocrine glands, which are situated in different separate regions of the body.

Internal organs can be divided into parenchymal and hollow (tubular) organs. Parenchymal organs consist of parenchyma, which is specialized tissue that carries out the specific function of the organ. Parenchymal organs always have a stromal capsule, which gives off connective tissue intercalations, or trabeculae, into the parenchyma. The stroma contains blood and lymph vessels, and nerves. It provides support and performs a trophic function. This group of organs includes the pancreas, the liver, the kidneys, the lungs and some other organs.

Hollow organs have a lumen and are shaped like tubes of different diameters. Despite some differences in their shape, the walls of tubular organs are similar in structure, and are formed by the following layers. The mucosa is the innermost layer; over it lies the submucosa, the muscularis and, on the outside, adventitia or serosa (Fig. 116). The walls of some tubular organs (trachea, bronchi) also contain a cartilage skeleton.

The mucosa (túnica mucósa) is the internal layer of tubular organs of the digestive, respiratory and urogenital systems. It consists of the surface epithelium and the lamina propria of mucosa. The surface epithelium lines the inside of the mucosa. Depending on its functions, the epithelium can be stratified squamous (oral cavity, pharynx, esophagus, and portion of rectum), transitional (urinary tract), and simple columnar, or prismatic

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Fig. 116. Structure of digestive tube. Transverse (A) and longitudinal (B) sections.

1 — mesentery; 2 — compound digestive gland; 3 — gland duct; 4 — epithelium of mucous membrane; 5 — submucous nervous plexus (Meissner’s); 6 — muscular-intestinal nervous plexus (Auerbah’s); 7 — longitudinal layer of muscular coat; 8 — circular layer of muscular coat; 9 — lamina propria of mucous membrane; 10 — solitary lymphoid nodule; 11 — submucosa; 12 — serous coat; 13 — mucous membrane; 14 — folds of mucous membrane; 15 — interstinal villi.

(stomach, intestine, trachea). It can also be stratified ciliary (nasal cavity, larynx). Epithelial cells are connected with each other by specialized cell junctions (tight junctions, desmosomes, etc.), and thus form a continuous layer. The epithelium protects the underlying tissues. In some organs (intestine, kidneys, stomach, etc) it performs selective absorption of substances. Among epithelial cells there are unicellular glands called goblet cells, which secrete mucus. Mucus keeps the mucosa moist, protecting the epithelium. Beneath the epithelium is the basement membrane.

The basement membrane is approximately 1 mm thick. It consists of an amorphous substance and fibrous (reticular) structures. It contains glycoproteolipid complexes. Basement membranes are perforated by many round or oval fenestrae, 2.5–4.0 mm in diameter. These windows correspond to the places of contact between the basal membrane and the processes of adjoining fibroblasts. The basement membrane acts like an elastic support for the epithelial layer and serves as a barrier during filtration or diffusion. It also participates in nourishment or the epithelium, which

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does not contain capillaries. One of the properties of the epithelium is polarity, which means that the basal and apical parts of the layer and of individual cells have a different structure. The epithelium is highly capable of regeneration.

Situated to the outside of the basement membrane is the lamina propria. It consists of loose fibrous connective tissue, which contains blood and lymph vessels, nerve fibers, lymphoid cells (lymphocytes, plasmocytes) and lymph nodules, and simple multicellular glands. The lamina propria supports the surface epithelium, provides it with nutrients and takes part in absorption of liquid and products of digestion (small intestine)

At the border between the mucosa and submucosa lies the muscular layer of the mucosa, formed by a thin layer of smooth muscle cells (1–3 myocytes thick). Some organs (tongue, gums) do not have this layer. During contraction of the muscular layer (l a m i n a m u s c u l a r i s m u - c o s a e) the mucosa forms folds.

There are two possible types of structure of the muscular lamina of mucosa. In organs which have simple epithelium, or the main function of which is absorption (stomach, small and large intestines), the myocytes of the lamina muscularis mucosae intertwine with each other, forming a network structure. In the organs, the main function of which is secretion, the smooth muscle cells have a more disorderly orientation.

The submucosa (téla submucósa) is situated on the outside of the mucosa. It consists of loose connective tissue, which is rich in elastic fibers. The submucosa contains a large number of blood and lymph vessels, which form vascular plexuses. Numerous nerve fibers form the submucosal (Meissner’s) plexus. Due to the elasticity of the submucosa, it can contribute to formation of folds of the mucosal layer. In organs, where the submucosa is thin, folds of the mucosa are very small or are not formed at all.

Like the mucosa, the submucosa contains different simple branched glands, which secrete mucus and some bioactive substances (digestive enzymes). Some glands (for example, large salivary glands) are situated near a hollow organ, and communicate with it by an excretory duct, which opens on the surface epithelium.

Glands may have different shapes. Multicellular simple glands have an unbranched excretory duct. Compound glands have a more complicated system of branched tubes and alveoli, which open into one common duct. The parenchyma of a gland consists of epithelial tissue, which forms its secretory units and the duct system. Each secretory unit consists of approximately 10–20 epithelial cells, situated on a basement membrane. Outside the basement membrane there are myoepitheliocytes (basket cells),

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which surround the secretory units with long cytoplasmic processes. Contraction of these processes, which contain contractile filament, promotes secretion to exit from the secretory cells into the lumen of the gland. Some glands (in walls of the esophagus, larynx and other organs) contain separate endocrine cells. The secretion of these cells (bioactive proteins, etc.) does not proceed into the excretory duct, but is absorbed by nearby blood and lymph capillaries.

The lumina of the secretory units form the initial parts of the gland ducts. The walls of these ducts are lined with epitheliocytes. In the beginning parts of the ducts of the epithelial cells also produce secretion. Small ducts join with each other, forming a common (main) excretory duct. This duct extends to the surface epithelium of a tubular organ. In some places it may have ampullar amplifications, which can serve as reservoirs for accumulation of secretion.

The connective tissue component of the gland (stroma) consists of a capsule and connective tissue septa, which divide the glandular parenchyma into sections. The stroma provides protection and support; it contains vessels and nerves, fibroblasts, mast cells and lymphoid elements. Large sections of glands are called lobes, and smaller sections are called lobules. The stromal trabeculae between lobes are called interlobar, while the trabeculae between lobules are called interlobular.

The muscularis externa (túnica musculáris) of tubular organs is made up of smooth muscle cells. Within the muscularis the myocytes form two layers. The internal layer is circular muscle, and the external layer is longitudinal muscle. Between the two layers there is a thin intermuscular connective tissue septa, which contains blood and lymph vessels, and a large number of nervous fibers, which form the myenteric plexus.

The muscularis layer of tubular organs carries out important functions. In the organs of the digestive tract it provides muscle tone and performs rhythmic contractions (peristalsis), by which the content of these organs is mixed and moved from the oral cavity towards the anal opening. In the respiratory organs the muscularis regulates the width of the lumina of bronchi. In the urogenital apparatus it regulates the lumina of the ducts of the urinary and reproductive systems.

The muscularis of the beginning and end sections of the digestive tract (mouth, pharynx, upper part of the esophagus, external sphincter of the rectus) and some parts of the respiratory pathways (larynx) contains striated muscle tissue, which we can contract voluntarily. In other tubular organs the muscular layer consists of smooth muscles.

In some places of the digestive tract the circular muscle layer of the muscularis forms thickenings called sphincters, which can narrow the lu-

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