LECTURE 3
OPERATIVE SURGERY OF THORAX
The thorax is shaped like a truncated cone, which is flattened from before backward and contains important organs of respiration, circulation and digestion. Its anterior wall is the shortest and is formed by the sternum and the anterior portions of the first 10 pairs of ribs, with their corresponding costal cartilages. The lateral walls are formed by the ribs, which slope obliquely downward and forward; the posterior wall is made up of the 12 thoracic vertebrae and the ribs as far as their angles.
Thoracic Lines
1 Midsternal line—bisects the sternum and corresponds to the midline of the back.
2. Sternal line— runs vertically downward over the edge of sternum
3. Parasternal line—lies midway between the midsternal and the mammary lines
4. Midclavicular line— runs vertically downward from the midpoint of the clavicle 5. Anterior axillary line—this runs through the anterior axillary fold.
6. Midaxillary line—this is dropped from the middle of the axillary space
7. Posterior axillary line—passes through the posterior axillary fold
8. Scapular line—this runs through the apex of the inferior angle of the scapula
9. Paravertebral line—opposite the tips of the transverse processes of the vertebrae (used in radiology).
10. Vertebral line— lies vertically over the transverse processes of the thoracic vertebrae.
Breast (Mammary Gland)
The mammary gland extends verticallyfrom the 2nd to the 6th rib inclusive and horizontally from the side of the sternum (parasternal) to the anterior axillary line. The greater part of the breast, about two thirds, rests on the pectoralis major muscle; and the rest, about one third, on the serratus anterior. The breast is hemispherical in shape, but tonguelike processes may extend upward, downward or medially from it; the most common of such processes is the socalled axillary tail of Spence.This is a prolongation of breast tissue from the upper outer part of the breast, which passes through an opening in the axillary fascia, called the foramen of hanger. Therefore, although the breast proper is superficial to the axillary fascia, the axillary tail is deep to this fascia. Such a process is in direct contact with the axillary glands; therefore, if it is enlarged it may be mistaken for an axillary tumor or for axillary lymph adenopathy. Since the breast is a modified sebaceous gland, it lies in the superficial fascia and not upon or deep to it. The deep surface rests on the fasciae which cover the pectoralis major and the serratus anterior muscles. The gland is made up of lobes (usually 12) which are subdivided into lobules, and these in turn are composed of acini. The lobes are arranged like the spokes of a wheel which converge on the nipple, and each lobe is drained by a lactiferous duct; from 12 to 20 such ducts open onto the nipple. The organ is fixed to the overlying skin and the underlying pectoral fascia by fibrous bands known as Cooper’s ligaments. These are clinically important because cancer cells invade them and subsequently cause their contraction, which results in dimpling of the skin or fixation of the growth. By the same process, a malignant tumor may be fixed to the underlying pectoral fascia and then cannot be moved in the long axis of the muscle. The ducts open independently of each other on the surface of the nipple, and each has a dilated ampulla just before it ends. The nipple is conical in shape and usually is found in the 4th intercostal space. Its base is surrounded by a circular pigmented area called the areola, which has many small rounded elevations (cutaneous glands) known as the areolar glands of
The congenital abnormalities which may occur are:
1. Polymastia. This condition presents more than one breast on one or both sides and is due to the persistence of part of the milk ridge. The accessory breast may be well developed or tiny, and instances have beeoted where these breasts have been used for suckling. As many as 10 have been recorded in one individual.
2. Polythelia. This condition is one in which supernumerary nipples are found over a given breast and not necessarily on the milk ridge.
3. Gynecomastia. This is the presence of a female breast or breasts in the male. Congenital absence, amastia, either unilateral or bilateral, has also been recorded. Unilateral amastia is believed to be due to pressure of an arm in utero against the pectoral region. When this exists the pectoral muscles on the affected side are also atrophic or absent.
VESSELS, NERVES AND LYMPHATICS
Arteries. The arterial supply is derived chiefly from two sources: namely, the anterior perforating branches of the internal mammary artery and mammary rami of the axillary or one of its main branches. The anterior perforating arteries are branches of the internal mammary. The first 4 or 5 of these supply the breast, but only 2, usually the 1st and the 4th (or the 2nd and the 3rd) are well developed. The lateral thoracic artery, a branch of the second part of the axillary. Mammary branches of this latter vessel also have a tendency to travel transversely across the breast and in this way anastomose with the mammary rami of the perforating arteries. The thoraco-acromial artery, also a branch of part two of the axillary, is usually described as being one of the vessels which supply the breast tissue. Therefore, blood is supplied to the breast from two arterial sources: (1) the anterior perforating branches of the internal mammary and (2) the lateral thoracic arteries. Since these vessels pass cephalad to the nipple and in a transverse direction, the blood supply of the gland is located mainly at its superomedial and superolateral aspects. Therefore, an incision into the breast should be placed below the nipple to preserve the blood supply and to make the scar less visible. Since no major vessels reach the gland from its inferior aspect, plastic procedures, plastic procedures on the pendulous breast as well as diagnostic incisions into the breast should be placed in the inferior quadrants,
Veins. Although the main veins follow the arterial pattern just described, many of the smaller veins resemble the lymphatics and form a plexus beneath the areola. These are especially visible in the lactating breast. Large veins pass from the plexus toward the periphery and end in the axillary and the internal mammary veins.
Lymphatics. The lymph drainage consists of 3 parts: cutaneous, areolar and glandular. The cutaneous lymphatics carry the lymph from the integument of the breast, with the exception of the areola and the nipple, and converge in collecting trunks, which flow into the axillary glands of the same side. At the inner quadrants, and especially those near the sternum, lymphatics may cross and terminate in the breast or axillary glands of the opposite side. The areolar lymphatics drain the nipple and the areola and pass into the subareolar plexus of Sappey. The plexus is drained by two main lymph channels: one for the inner part and one for the outer. They usually unite into one main trunk, which passes to the anterior group of axillary glands. The anterior axillary (pectoral or superficial) set is really the main group and is placed under the anterior axillary fold, following the course of the lateral thoracic vein. These glands are found in the region of the 3rd rib. From this set the glands drain to the central axillary set, which is situated in the fat of the upper part of the axilla, under the axillary tuft of hair and along the inner border of the axillary vein. The intercostohumeral nerve passes outward between these glands, and enlargement of the latter may produce pressure on the nerve, resulting in pain along the axilla or inner border of the arm. From here the lymph vessels pass to the deep axillary glands, part of which form a lateral group which passes along the course of the axillary vein; the other part forms the apical group which has also been referred to as the infraclavicular glands. These glands lie behind the costocoracoid membrane. Therefore, it is impossible to free them adequately unless the whole region of the costocoracoid membrane is removed. The deep axillary glands become continuous with the deep cervical glands in the supraclavicular fossa. Although the above path is the usual one taken, there are other lymphatic zones of cancer spread. Some of the lymphatics from the upper and the outer quadrants of the breast form a trunk that pierces the pectoralis major muscle and directly enters the gland along the axillary vein, thereby short-circuiting the axilla. Lymphatics also leave the inner quadrant of the breast and reach the glands inside of the chest cavity, lying on each side of the internal mammary artery. Occasionally, a few vessels pass to the cephalic gland which lies in the deltopectoral groove. In some instances breast cancer may spread downward in the lymphatics to the epigastric region and there invade the abdominal wall. Development of metastases in the liver and in the pelvic cavity can be explained by such permeation. It is possible for cancer from one breast to spread across the midline to the other subpectoral plexus, then to the opposite axilla and finally to the opposite breast. The pectoral lymph plexuses should not be regarded as separate systems but rather as communicating networks.
Nerves. The nerve supply of the skin of breast is derived from the anterior and lateral branches of the 4th to the 6th intercostals nerves, which reach it by way of the 2nd to the 6th intercostals.
SURGICAL CONSIDERATIONS
BREAST ABSCESS Breast abscesses may be subcutaneous, intramammary or submammary. The incision for a subcutaneous or inframammary abscess should be so placed that it radiates from the nipple but never transversely across the breast. If the abscess is deeper, submammary or retromammary, this incision is not utilized, but instead a thoracomammary approach in the inframammary fold is used. This is the same incision that is utilized for benign tumors of the breast, since practically any portion of the gland can be examined through it. With the breast retracted upward and medially, the incision is placed in the pigmented line. Then it is carried down to the underlying muscle, and the breast is displaced upward. The necessary procedure is done, be it draining an abscess or removing a tumor. The breast is permitted to fall back into its normal position where it is sutured.
RADICAL MASTECTOMY
Radical mastectomy can be outlined in 6 anatomic steps, each having 3 substeps. This is only a plan and may be altered to fit any standard technic. The plan is outlined as follows:
1. Incision: a. Coraco-umbilical line b. Mobilization of skin medially to the midline of the sternum c. Mobilization of skin laterally to the latissimus dorsi (posterior axillary fold)
2. Axillary Fascia Step: a. Incision of axillary fascia along the lower border of pectoralis major b. Division of the pectoralis major near its insertion, leaving the clavicular part intact c. Division and ligation of the thoracoacromial vessels and nerves
3. Clavipectoral Fascia Step: a. Incision into the clavipectoral fascia along the lower border of the pectoralis minor b. Division of the pectoralis minor muscle c. Insertion of the pectoralis minor utilized as an axillary vein splint
4. Axillary Vein Dissection: a. Clamp, cut and ligate all venous tributaries b. Axillary glands and fat dissected downward c. Subscapular vessels used as a guide to the thoracodorsal nerve
5. Posterolateral Dissection: a. Exposure of the subscapular muscle b. Exposure of the latissimus dorsi c. Exposure of rectus abdominis
6. Medial Dissection: a. Dissection of pectoralis major and minor muscles b. Clamp and ligate perforating vessels (especially Number 2) c. Remove mass en bloc and close
Incision. Many incisions have been advised; however, the one described extends from the coracoid process above, which is always palpable, to the umbilicus below, which is always visible. Forceps are placed in the breast, which is elevated, and then traction is made laterally; the incision is placed along the coraco-umbilical line. Next, traction is made to the opposite side, and the incision is completed along the coraco-umbilical line. The lateral and medial skin flaps are formed; they extend medially past the midline of the sternum and laterally to the latissimus dorsi.
Axillary Fascia. The second step is the axillary fascia phase. This fascia provides a covering for the pectoralis major muscle. incision is placed into the fascia along the lower border of the pectoralis major. he index finger of the left hand is placed through the defect and is guided, not to the deltopectoral groove, which seems natural, but rather to the claviculosternal groove, which is not as well marked. If the clavicular portion of the pectoralis major muscle remains intact, it protects the cephalic vein, which runs in the deltopectoral groove. In the course of the operation it might become necessary to ligate or remove the axillary vein; if the cephalic vein is intact, the venous return of the superior extremity will not be impaired. The pectoralis major is cut near its insertion, and its sterno-abdominal part is reflected medially. As the pectoralis major is reflected medially, the thoraco-acromial vessels and the anterior thoracic nerves appear as a neurovascular bundle along the medial border of the pectoralis minor. These are clamped, severed and ligated.
Clavipectoral Fascia. The third step is the clavipectoral fascia phase. This fascia provides the covering for the pectoralis minor muscle. It is incised along the lower border of the pectoralis minor, so that the index finger of the left hand may be slipped under it and around the muscle. The pectoralis minor is divided, but a small part is left attached to the coracoid process; this acts as a splint for the axillary vein. With both pectoral muscles divided and retracted medial and downward, the axilla is exposed and then is ready for dissection of its contents.
Axillary Vein Dissection. In the axillary vein phase, the axillary sheath which covers the vein is opened carefully, and the vascular branches below the vein are individually identified, cut and tied. These usually include the short thoracic vein, the lateral thoracic artery, the long thoracic vein, the subscapular vein, the lateral thoracic vein and the subscapular artery. The axillary lymph glands and fat are dissected downward. The subscapular vessels act as a guide to the thoracordorsal nerve, and the lateral thoracic artery is the guide to the long thoracic nerve. If possible, these nerves should be saved, but if they are involved they must be sacrificed
Posterolateral Dissection. This is carried out next. After the axillary cleansing has been accomplished, the subscapular muscle, the teres major and the latissimus dorsi come to view; the rectus sheath is also exposed.
Medial Dissection. This is the final stage. The origins of the pectoralis major and minor are severed, the mass is retracted laterally and downward, and the erforating vessels are sought in the intercostal spaces; they are found close to the lateral margin of the sternum. These must be clamped, cut and ligated, with special mphasis being placed on perforating branch Number 2, which has been discussed thoroughly. The entire mass is removed en bloc, and the wound is closed. At times skin grafts may be necessary. Currently, supraradical mastectomy is advocated by some surgeons for carcinoma of the breast. These procedures vary according to one’s definition of “radical.” Some surgeons advocate internal mammary artery (lymph node) dissection, removal of the clavicle, the ribs, and/or the superior extremity. This has become an individual problem and decision.
Diaphragm
The word diaphragm is derived from the Greek “dia” (in-between) and “phragma” (fence). It is a dome-shaped, musculo-aponeurotic partition which is located between the thorax and the abdomen.
This musculotendinous partition is located between the pleurae and the pericardium above and the peritoneal cavity below. When relaxed and viewed from below, it forms a dome-shaped roof for the abdomen. Its circumferential part is fleshy, and these muscle fibers curve upward and inward from every side to join the edges of an aponeurotic sheath called the central tendon. It is this tendon which acts as the site of insertion for the diaphragm. The central tendon is strong, its tendinous bundles passing in different directions and interlacing with one another, giving it a pleated appearance. At times it has a trilobite appearance. Its median part is wide and is called the median lobe; the extremities or horns of the tendon are referred to as the right and the left lobes. The latter is the narrower. The tendon is inseparably blended above with the fibrous layer of the pericardium.
Origin. The origin of the diaphragm is quite extensive and takes place at the circumference of the thoracic outlet. It is best to consider it as originating at 4 points: sternal, costal, the crura, and the medial and lateral arcuate ligaments. The sternal origin consists of short right and left slips from the posterior aspect of the xiphoid process which are separated from each other by a little areolar tissue. These fibers pass upward and backward to the anterior margin of the central tendon where they insert. The costal origin is extensive and rises at a very steep angle. It usually consists of 6 fleshy muscle bundles which arise from the deep surface of the lower 6 costal cartilages, interdigitating with the costal origin of the transversus abdominis muscle. These fibers insert into the lateral and anterior borders of the central tendon. The crura are long tapering bundles which are fleshy above and tendinous below. The right crus arises from the sides of the bodies of the upper 3 lumbar vertebrae and the intervertebral disks; the left arises from the upper 2 lumbar vertebrae. The medial fibers of the 2 crura decussate in front of the commencement of the abdominal aorta; the fibers of the right crus encircle the esophagus. Both crura ascend forward and reach the posterior border of the central tendon.
Ligaments. The lateral and medial arcuate ligaments (lumbocostal arches) are lateral to the crura. The medial arcuate ligament is the upper thickened border of the psoas fascia which stretches between the side of the body of the 2nd and the tip of the transverse process of the 1st lumbar vertebrae. The lateral arcuate ligament is the thickening of the anterior lamella of the lumbar fascia which extends from the tip of the first lumbar transverse process to the lower border of the last rib. From this origin, the muscle fibers arch upward to reach the posterior border of the lateral part of the central tendon.
Nerves. The nerve supply of the diaphragm is derived from the right and the left phrenic nerves (C3, C4, C5).
Arteries. The arteries that supply it are the pericardiophrenic, the inferior phrenic, the musculophrenic and the intercostals
Actions. The diaphragm is the chief muscle of respiration and it is in the abdominal type of breathing that it plays its greatest role. When its fibers contract, they straighten out, so that the domelike appearance is lost. In deep inspiration, the central tendon descends for a short distance
FORAMINA (OPENINGS)The continuity of the diaphragm is broken by 3 large apertures and several smaller ones. The large openings accommodate the aorta, the esophagus and the inferior vena cava. The thoracic levels at which these structures pass are: the inferior vena cava at the 8th thoracic, the esophagus at the 10th and the aorta at the 12th.
Aortic Opening. This is located in the median plane in front of the lower border of the 12th thoracic vertebra and between the crura. It is bounded anteriorly by a tendinous arch which connects the medial borders of the crura to each other. Through this orifice pass the aorta, the thoracic duct and the azygos vein. The thoracic duct and the azygos vein are covered by the right crus.
Esophageal Opening. This oval aperture lies opposite the 10th thoracic vertebra in front, to the left of the aortic opening and behind the central tendon. The descussating fibers seem to act as a sphincter for the cardiac end of the stomach and prevent itscontents from returning to the esophagus. In addition to the esophagus, it transmits the right and the left vagus nerves and the esophageal branches of the left gastric artery with its companion veins. In cirrhosis of the liver, when an obstruction to the portal system is present, these veins at the lower end of the esophagus become dilated and varicosed, and frequently rupture. The vagi do not run to either side of the esophagus but are situated so that the left vagus passes anteriorly and the right posteriorly. The left, being anterior, supplies the anterosuperior surface of the stomach, and the right innervates the posteroinferior. The position of this opening is somewhat variable, since it may be found in the median plane or even to the right of it and may be very close to the aortic opening.
Inferior Vena Cava Opening. This opening is wide, and about
Costophrenic Recess. The costophrenic recess is that portion of the pleural cavity which is unoccupied by lung except after full inspiration. Here the diaphragmatic
pleura is in contact with the costal pleura. When in full inspiration, the inferior border of the lung insinuates itself into this recess, and retraction of the overlying intercostals spaces is seen externally as the diaphragm decends and opens the costophrenic recess
Pleural Cavities and Pleurae
VISCERAL AND PARIETAL PLEURAE The thoracic cavity is divided into right and left pleural cavities and a region situated between these called the mediastinum. The lung invaginates the pleural cavity so completely that only a potential space remains, and by this process the pleura becomes divided into visceral (lung) and parietal (wall) layers.
The visceral pleura invests the lung, dips into its fissures and adheres so firmly that it is impossible to strip it from lung tissue.
The parietal pleura is subdivided, according to location, into 4 parts: costal, cervical, diaphragmatic and mediastinal. The costal pleura lines the ribs and their cartilages, the sides of the vertebral bodies and the back of the sternum. This is the thickest of all the parietal pleurae and is separated from the thoracic wall by the thin endothoracic fascia. It is directly continuous above with the cervical pleura (cupola) which covers the apex of the lung. This portion of the pleura extends upward into the root of the neck behind the interval between the two heads of the sternocleidomastoid muscle. Posteriorly, it reaches the level of the head of the 1st rib, but anteriorly it rises about 1 1/2 inches above the sternal extremity of that rib. Hence, it is protected by the rib posteriorly but not so anteriorly. This is explained by the fact that ribs do not run horizontally but obliquely; there is a drop of about 1 1/2 inches between the vertebral and the sternal attachments of the 1st rib. The upper aspect of the cervical pleura is covered by a layer of connective tissue called Sibson’s fascia. This fascia forms the internal lining of the scalene muscles and spreads out, fanlike from the transverse process of the 7th cervical vertebra to the inner border of the 1st rib. It separates the pleura from the first part of the subclavian artery, the phrenic nerve and the internal mammary artery. The diaphragmatic pleura is thin and very adherent to the diaphragm; it covers that part of the diaphragm not covered by the diaphragmatic pericardium. It is continuous with the costal pleura laterally, but medially it becomes continuous with the mediastinal pleura. The diaphragmatic pleura meets the costal pleura in 2 places: behind the sternum (sternal reflection) and in front of the bodies of the thoracic vertebrae (vertebral reflection). At the point at which the visceral pleura meets the mediastinal layer of parietal pleura there forms a pleural passageway. The upper part of this passageway contains those structures constituting the root of(the lung (pulmonary vessels and bronchus). The lower part is empty; hence, its walls approximate each other and form the pulmonary ligament. Only after deep inspiration are the lungs and the parietal pleurae completely in contact with each other. In ordinary breathing the lungs are not completely expanded; therefore, the edges of the pleurae fall together, preventing the formation of a cavity. This touching of the pleurae takes place mainly along the anterior and lower borders. During quiet respiration the costal and the diaphragmatic pleurae remain in apposition below the lower border of the lung. The space thus formed is known as the costodiaphragmatic recess. It is about
SURFACE MARKINGS The surface markings of the lungs and the pleurae are of diagnostic value and can be constructed in the following way: The junction of the costal and the mediastinal pleurae (costomediastinal line of pleural reflection) is not the same on both sides of the body. On the right, it starts about 1 1/2 inches above the sternoclavicular joint and passes to the middle of the manubrium opposite the 2nd costal cartilage. From this point it drops vertically near the midline of the sternum to the xiphosternal joint, where it becomes continuous with the costodiaphragmatic line of reflection. On the left side, the line of pleural reflection is the same until the 4th interspace. Here it curves outward to the left border of the sternum along which it descends to the xiphosternal junction. It becomes continuous with the costodiaphragmatic line of reflection just as it does on the opposite side. The junction of the costal and the diaphragmatic pleurae (costodiaphragmatic line of pleural reflection) may be marked by a line which starts at the xiphosternal joint and passes posteriorly to the 12th thoracic vertebra, the line being convex downward.
RIBS (COSTAE) The 12 pairs of ribs form a series of obliquely placed bony arches which constitute the greater part of the wall of the thoracic cage. They overhang the upper part of the abdomen, articulate with vertebrae posteriorly and end in costal cartilages anteriorly. They increase in length from the 1st to the 7th and then become progressively shorter.
True Ribs. The first 7 pairs are called true ribs because their cartilages articulate with the sternum.
False Ribs. The cartilages of the last 5 pairs are known as false ribs.
The blood supply reaches each rib through its owutrient vessel which enters just beyond the tubercle and runs forward as far as the inner extremity of the bone . An additional supply is obtained from the periosteal vessels. The periosteum of the ribs strips easily from the bone, but that of the sternum does not. H. A. Harris has pointed out that no anastomosis occursbetween the vessels of the diaphysis and the epiphysis of the ribs and that the vessels of the former are virtually “end arteries.” Ossification resembles the long bones of the limbs and the bodies of the vertebrae, since it begins to take place in the 2nd fetal month. The process begins near the angle and continues in both directions but fails to reach the sternal end, resulting in costal cartilages.The ribs, the vertebrae, the sternum and the diploe of the skull are filled with the red blood-forming marrow. It is in these bones and not in the limbs that the blood elements are formed after puberty
SURGICAL CONSIDERATIONS
FRACTURED RIBS The ribs which are usually fractured are the 3rd to the 8th; ribs 1 and 2 and those below the 8th are infrequently involved. The fracture of the bone proper is of no great importance with the exception of the local discomfort which it produces. However, complications such as puncture of the pleura, the lung, the liver or the spleen, as well as diaphragmatic hernia, secondary pleural effusion and surgical emphysema may result in serious sequelae. Little displacement or shortening occurs in rib fractures because of the attachment of the intercostal muscles and fixation of both rib extremities.
ASPIRATION OF THE CHEST The chest is aspirated as either a diagnostic or a therapeutic procedure. It is performed best with the patient seated and with the arm of the involved side placed on the opposite shoulder. If this is impossible, the aspiration may be done with the patient lying on the uninvolved side. The site of election is usually a little posterior to the posterior axillary line in the 6th, the 7th or 8th intercostal space. Some prefer the midaxillary line. The needle should be passed little toward the superior surface of the lower rib so that the intercostal artery and nerve are not injured.
THORACOSTOMY Thoracostomy is an opening made through, the chest wall for the purpose of drainage.It may be a closed (interspace) or an open (rib resection) drainage. The indication for such drainage is usually empyema.
Closed Method. This is usually made in the 7th or 8th interspace in the midaxillary line or in line with the angle of the scapula. Procaine is injected at the selected site, and asmall stab incision is made. A trocar is inserted just over the rib, thus avoiding the intercostal artery, vein and nerve which lie on the undersurface of the rib. This is advanced into the pleural space where the fluid is located. The obturator is withdrawn, and a catheter is inserted. Then the trocar is drawn over the catheter, which fits snugly and may be fixed by pins or a suture.
(Rib Resection) and Thoracoplasty. This method necessitates the resection of a piece of rib. The angle of the scapula is palpated, and then the patient’s arm is elevated and placed to the opposite side. The rib immediately below this point is usually selected as the one suitable for resection. If the rib above is chosen, the scapula may act as a shutter; if a rib much lower is selected, an inadvertent transthoracic laparotomy may be performed. An incision is made directly over the rib selected, the soft tissues are divided to the periosteum, which is completely freed, and about 2 to
INTERCOSTAL SPACES MUSCLES The muscles which are associated with the intercostal spaces are the external intercostal, the internal intercostal and the transverses thoracis. Corresponding intercostal nerves and vessels supply them The external intercostal muscle fibers are the thoracic representative of the external abdominal oblique. They pass downward and forward between adjacent borders of 2 ribs and become membranous in the intercartilaginous portion of the space where they assume the name of the anterior intercostals membrane. The fleshy interosseous parts extend as far as the tubercles of the rib posteriorly. The internal intercostal muscle is the thoracic representative of the internal abdominal oblique. These fibers run in the opposite direction to those of the external. The fleshy fibers extend from the sternal ends of the spaces as far as the angles of the ribs posteriorly; here they become membranous and continue as the posterior intercostal membrane, which merges with the anterior costotransverse ligaments.
The transversus thoracis muscle is the thoracic representative of the transversus abdominis and should be considered as having 3 parts: the sternocostalis, the innermost intercostal and the subcostal
The subcostal groove in a typical rib is situated on the deep surface of its sharp lower border. It contains from above downward the respective intercostal vein, artery and nerve (V.A.N.). In the posterior part of the space the nerve is situated midway between the ribs, but from the angles of the ribs forward it lies in the subcostal groove
BLOOD VESSELS
Intercostal Arteries. Since there are 11 intercostal spaces, there must be 11 intercostal arteries. These originate posteriorly and are designated as the posterior .intercostals arteries. The anterior intercostal arteries arise from the internal mammary. Not all 11 posterior arteries arise from the aorta, since only the lower 9 have this origin; the upper 2 are branches of the highest intercostal, a branch of the costocervical trunk of the subclavian. The right aortic intercostals are longer than the left because of the position of the aorta to the left of the vertebral column. Each vessel divides into anterior and posterior branches. The posterior supplies the spinal canal, the back musculature and the overlying skin. It is the anterior branch of the posterior intercostals artery which passes forward in the subcostal groove. The intercostal vessels and their corresponding nerves pass anteriorly in the plane between the innermost intercostals and the internal intercostal muscles. The lower intercostal vessels and nerves occupy a corresponding plane in the abdominal wall. Anteriorly, the vessel divides into superior and inferior (collateral) branches which unite with those from the internal mammary artery. Since the lowest two intercostal spaces remain open, the lowest two intercostal arteries continue on into the abdominal wall
The subcostal artery is the same as any intercostal artery, but since there is no 12th space, it assumes a separate name.
