CHAPTER IX.

THE VASCULAR SYSTEM.

=The Vascular System.=—The vascular system is composed of the organs immediately concerned in the circulation throughout the body of the fluids which convey to the tissues the nutritive substances and oxygen necessary for their metabolism and carry from them to the excretory organs the waste products formed during metabolism.

The system is usually regarded as being composed of two portions, the one consists of organs in which circulate the red fluid which we term blood, and called the _blood vascular system_, while the organs of the other contain a colorless or white fluid known as lymph or chyle, and is known as the lymphatic circulation.

{ arteries { Blood vessels { capillaries The vascular { The blood vascular system { { veins system { { Heart { The lymphatic circulation

=The Blood Vascular System.=—A knowledge of the general features of the circulatory system are essential to the undertaker and the embalmer as a means of enabling him not only to perform the ordinary operations and duties of his profession intelligently, but to equip him with the knowledge necessary to meet the exceptional conditions which sometimes arise.

There is a growing appreciation of the fact, also, that thoroughness in the practice of embalming is worth striving after. Many cases of embalming, no doubt, require a minimum amount of attention, particularly where the body is to be kept but a short time. Where preservation for longer periods is required, as for transportation, or where disease and accident have interfered seriously with the circulation, a more exact knowledge is evidently desirable.

The blood vascular system comprises the heart, which is the central organ of the whole system, and all the blood vessels. This system, with its arteries and veins, permeates the whole body and becomes divided and subdivided at its outer portion into vessels constantly decreasing in size, until those extremely minute vessels, the capillaries, are reached. All the tissues of the body are very rich in these, so that all portions of the body are supplied with blood, which is essential for the nourishment and rebuilding of the tissues. The large vessels which convey blood from the heart are termed arteries, while the vessels which convey the blood back to the heart are termed veins.

For one to properly embalm the human body, it is necessary to understand the way the fluid will circulate through the body, and the only way we can do this is to study the circulation of the blood as it would occur in life.

To facilitate the description of the blood vascular system, it has been divided into six subdivisions as follows:

(1) Systemic. (2) Pulmonary. (3) Coronary. (4) Portal. (5) Foetal. (6) Collateral.

=The Systemic Circulation.=—The systemic circulation is called the greater circulation of the body. The course of the blood is from the left ventricle of the heart through the aortic semi-lunar valve to the great aorta and its branches which end in capillaries in the tissues of the body then through the veins the terminal trunks of which end in the right auricle of the heart. So the systemic circulation is the circulation of the blood from the left ventricle of the heart to the right auricle of the heart and this circulation has the important function of carrying oxygen to the tissues to nourish them, and of carrying carbonic acid gas back to the heart which is a waste product of the tissues.

The systemic circulation is divided for the sake of convenience into the following:

(1) The arterial system. (2) Capillary. (3) The venous system.

=The Arterial System.=—The blood leaving the heart passes from the left ventricle through the aortic semi-lunar valve, into the ascending aorta. Here the two coronary arteries come off which go to supply the muscular tissues of the heart. The ascending aorta passes into the arch of the aorta. Here are given off the innominate artery to the right and the common carotid and the subclavian to the left. The innominate is only about an inch or two in length, and divides into the right common carotid and the right subclavian arteries. On each side the subclavian passes down beneath the clavical bone and enters the axillary space where it is known as the axillary artery. After leaving the axillary space, the artery passes down the arm and is known as the brachial artery. About one inch below the bend of the elbow the artery divides into two branches, known as the radial and ulnar. The radial goes to the thumb side of the hand, and the ulnar to the little finger side of the hand. The ulnar artery and a branch of the radial form the palmar arch, which gives off the branches to the fingers. Coming off the brachial are the deep brachial arteries and the anastomotica magna arteries which anastomose and give collateral circulation to the forearm, by means of the recurrent radial and ulnar arteries.

The common carotid arteries pass up each side of the neck to a point opposite the Adam's apple, where they, divide into the external carotid, which supplies the muscular tissue of the face, and the internal carotid artery, which goes up through the skull and helps to form the circle of Willis.

The vertebral arteries come off the subclavian arteries on either side and pass upward, winding through the foramen of the vertebrae, until finally arriving inside the cranial cavity, unite to form one artery called the basilar, which helps to form the circle of Willis.

The circle of Willis is situated at the base of the brain and gives off to the front the two anterior cerebral arteries, to the sides the two middle cerebral arteries, and to the back the two posterior cerebral arteries. The two anterior cerebral arteries are connected by the anterior communicating branch, and the middle cerebral artery and the posterior cerebral arteries on each side are connected by the posterior communicating branches. The cerebral arteries terminate in the piamater as a dense capillary network, and from there supply the substance of the brain with nutrition.

The external carotid artery supplies the muscular tissues of the face. The external carotid artery arises from the common carotid artery at about the level of the upper border of the thyroid cartilage—a level which corresponds with the body of the fourth cervicle vertebra. Thence it is directed upward and slightly backward towards the angle of the jaw, where it enters the substance of the parotid gland and continues upward in that structure to just below the root of the zygoma. Here it gives rise to a large branch, the internal maxillary, and is then continued upward over the root of the zygoma upon the side of the skull, this terminal portion of it being termed the superficial temporal artery. The branches of the external carotid artery from below upward are (1) the ascending pharyngeal, (2) the superior thyroid, (3) the lingual, (4) the occipital, (5) the facial or external maxillary, (6) the posterior auricular, (7) the internal maxillary, (8) the superficial temporal.

The arch of the aorta now continues into the thoracic aorta, so called while it is in the thoracic cavity, and after it has passed through the diaphragm becomes the abdominal aorta. At a point opposite the umbilicus or navel the abdominal aorta divides into the two common iliac arteries. Each common iliac artery divides into an internal iliac artery, which supplies the organs of the pelvic cavity, and an external iliac artery, which passes beneath Poupart's ligament. As the artery passes down the leg it is known as the femoral artery, until it passes into the popliteal space, where it is called the popliteal artery. About one inch below the popliteal space the artery divides into the anterior tibial artery, which runs on a straight line down the front and outside of the leg to a point between the big toe and the one next to it, and the posterior tibial artery which passes down the back part of the foreleg between the inside ankle and the heel. The peroneal, a branch of the posterior tibial, passes down the foreleg between the outside ankle and the heel. The anterior tibial artery, as it passes through the instep is known as the large dorsal artery and further on is known as the small dorsal artery. In the foot is the plantar arch, formed by branches of the posterior and anterior tibial arteries, which send out branches to each toe.

Coming off the femoral are the deep femoral and the anastomotica magna arteries, which anastomose and form collateral circulation to the foreleg by means of the recurrent anterior and posterior tibial arteries.

Coming off the subclavian arteries are the superior and inferior mammary arteries, which pass down over the chest wall, anastomose and give collateral circulation to the lower extremities by means of the superior and inferior epigastric arteries, branches of the external iliac and femoral arteries.

The thoracic aorta gives off the intercostal arteries, which supply the ribs, the bronchials which supply the lungs, the esophageal which supplies the esophagus, and the pericardiac which supplies the pericardium.

The abdominal aorta gives off in rotation the coeliac axis, which as a hub in a wheel gives off three spokes, the gastric artery to the stomach, the hepatic to the liver, and the splenic artery to the spleen. The next branch is the phrenic, which supplies the diaphragm, then the suprarenal artery, two or more in number coming off of both the aorta and the renal arteries. The suprarenal arteries supply the suprarenal capsules. The next branch is the superior mesenteric artery, which supplies the small intestines; the next branch is the renal arteries, which supply the kidneys; the next branch is the spermatic or the ovarian arteries, which supply the testes in the male or the ovaries in the female; the inferior mesenteric artery, which supplies the large intestines. Also coming off the aorta at regular intervals are the lumbar arteries, which supply the side walls.

=The Capillary Circulation.=—The capillaries are very minute blood vessels, forming a network between the terminating arteries and the commencing veins.

They derive their name from the word capillus (hair). They vary in size from 1-3500 to 1-3000 of an inch, the largest capillaries being those of the skin. These little vessels are so thickly distributed throughout most of the tissues of the body as to make it impossible to insert a cambric needle in the flesh without pricking scores of them.

When we embalm a body the object should be to introduce a sufficient amount of fluid through the arterial system so that these tiny capillaries will be filled. These little vessels are so minute and the walls are so thin that the fluid is immediately taken up into the tissues. If every tissue of the body can be supplied with fluid by means of the capillaries, we would have the ideal, the body would be perfectly embalmed. Let us then not only be arterial embalmers, but, better still, let us be capillary and tissue embalmers.

Capillaries have one wall, which is the continuation of the inner wall of the artery, thus making the capillary so thin that fluid finds its way easily through it into the surrounding tissues.

Some parts of the body are more vascular than others and some tissues of the body, such as the cornea of the eye, the epidermis, cartilage, the substance of the brain, etc., are entirely destitute of capillaries.

The combined area of all the capillaries of the body is many times greater than the combined area of the trunk vessels. If this were not so, the high pressure on the arterial system would break the thin capillary walls and also the greater area allows the blood to circulate more slowly which gives time for the liberation of oxygen to the tissues and for the absorption of carbon dioxide.

=The Venous System.=—The veins, like the arteries, are tubular vessels, their function being to receive the blood from the capillaries and convey it to the auricles of the heart. There are two classes of veins, =systemic= and =pulmonic=.

The systemic veins receive the impure or carbonized blood from the capillaries and convey it to the right auricle of the heart.

The pulmonic veins receive the pure oxygenized blood from the lungs and convey it to the left auricle of the heart. The pulmonic veins will be taken up and discussed later under the pulmonary circulation.

_Systemic veins_ are divided into superficial and deep veins and sinuses.

_The superficial veins_ are found between the layers of the superficial fascia, just beneath the skin, and communicate with the deep veins by branches which pierce the fascia.

_The deep veins_ are found deeper down, between the muscles, and are surrounded by the deep fascia.

The smaller arteries, such as the radial, brachial, posterior and anterior tibial, and the peroneal arteries, are each accompanied by two veins, one on each side of the artery, which are called venae comites (accompanying veins). The larger arteries, such as the common carotid, the femoral and the iliac, are accompanied by only one vein.

Veins arise from the capillaries, or, rather, from the minute capillary plexus, formed by a massing or blending of the tiny venules. These small vessels unite to form larger trunks, and as they continue toward the heart increase in size until they finally unite to form the ascending and descending venae cavae.

_The Sinuses._—The cerebral veins are small vessels that arise from the capillaries of the brain, and terminate in the sinuses of the dura mater. There are many sinuses in the cranial cavity, and differ from the vein, in that the walls are thinner, having only two walls while the veins have three, and they do not have valves. The outer walls of the sinuses of the brain are formed by a division of the dura mater, while the inner wall is the continuation of the inner wall of the vein.

They are of little interest to embalmers, except for the fact that when the brain is injected by any of the so-called needle processes, the fluid is quickly conveyed through these vessels to the tissues of the brain, and that organ is thoroughly preserved.

The vessels starting at the foot are the anterior and posterior tibial veins, which unite just below the knee to form the popliteal vein, in the popliteal space. Another vein starts from the foot and runs into the popliteal vein called the external short saphenous. Starting also at the foot and running into the posterior tibial vein is the peroneal vein.

The popliteal vein after leaving the popliteal space is known as the femoral vein as it passes up the leg, to Poupart's ligament. Another vein, the internal long saphenous, starts at the foot, and runs into the femoral vein about an inch below Poupart's ligament. After passing beneath Poupart's ligament the vessel is called the external iliac. Coming from the organs of the pelvic cavity is the internal iliac, which joins with the external iliac vein to form the common iliac vein. The right and left iliac veins join opposite the umbilicus to form the ascending vena cava. The ascending vena cava passes upward to the right of the vertebral column through the diaphragm and enters the right auricle of the heart by means of the eustachian valve.

In the forearm are the radial veins on the thumb side of the hand, the ulnar veins on the little finger side of the hand, and the median vein just between the radial and ulnar veins. The median vein divides into the median cephalic vein and the median basilic. The median cephalic vein unites with the radial vein to form the cephalic vein, which runs up the back part of the arm and finally empties into the subclavian vein. The median basilic unites with the ulnar vein to form the basilic, which runs up the inner part of the arm between the biceps and triceps muscles. The deep brachial veins or the vena comites, two in number, which follow the brachial artery, run into the basilic vein. When the basilic vein arrives at the axillary space it takes on the name of the axillary vein, and as the vessel passes beneath the subclavian bone, it becomes the subclavian vein. The right and left subclavian veins with the right and left internal jugular veins from each side of the head form the right and left innominate veins, which unite to form the descending vena cava, which runs into the right auricle of the heart.

Starting at the head, the superior longitudinal sinus begins at the fore part of the brain and runs backward between the two hemispheres of the brain and empties into the wine press or Torcular herophili. The inferior longitudinal sinus begins at the fore part of the brain, but rung deeper down in the pia mater between the two hemispheres of the brain, terminates in the straight sinus which empties into the wine press. Beginning at the base of the cerebellum are the two occipital sinuses which run together and terminate in the wine press. After all the blood has been gathered together in the wine press, it leaves by means of the right and left lateral sinuses which pass down as far as the jugular foramen. Beginning at the base of the brain in front are the right and left cavernosus sinuses, which run into the inferior petrosal sinuses, which pass down as far as the jugular foramen, where they join the lateral sinuses to form the right and left internal jugular vein. The superior petrosal sinus is between the lateral sinus and the cavernosus sinus uniting them. Joining the right and left cavernosus sinuses is the circular sinus and joining the right and left inferior petrosal sinuses is the transverse sinus. The right and left internal jugular veins pass down through the jugular foramens and down the neck to where they with the right and left subclavian veins form the right and left innominate veins. The right and left innominate veins unite to form the descending vena cava which empties into the right auricle of the heart.

Beginning in the tissues of the heart are the coronary veins, which terminate in the coronary sinus and then into the right auricle of the heart through the coronary valves.

The azygos system consists of the major azygos vein, which starts at the right external iliac vein and empties into the descending vena cava; the minor azygos vein which starts at the left external iliac vein and empties into the major azygos vein back of the heart; and the tertiary azygos vein, which starts at the left subclavian vein and empties into the minor azygos vein. The azygos veins collect all the blood from the side walls of the body and form a perfect collateral circulation between the superior and inferior caval systems, and thoroughly equalizes the blood pressure all over the body. The major azygos vein receives the following: the right intercostal veins, excepting the first; the azygos minor; the right bronchial vein; the esophageal vein; the pericardiac; and the posterior mediastinal veins. The minor azygos vein receives the following: the tertiary azygos vein; the lower five left intercostal veins; the small left mediastinal veins; the lower left esophageal veins. The tertiary azygos receives the following: the fifth, sixth and sometimes the seventh intercostal veins; the lower end of the lower left superior intercostal vein; and the left bronchial vein. The inferior vena cava receives the following veins: the lumbar veins; the hepatic veins; the phrenic veins; the renal veins; the right suprarenal vein; the right spermatic or ovarian vein. The left spermatic or ovarian vein and the left suprarenal vein empty into the left renal vein.

=The Pulmonary Circulation.=—This is the circulation existing between the right ventricle of the heart through the lungs back to the left auricle of the heart.

The pulmonary artery takes its origin from the summit of the right ventricle. It is about two inches in length, and is directed upward, backward and slightly towards the left, and beneath the arch of the aorta it divides into the right and left pulmonary arteries. These end in a system of capillaries in between the air cells of the lungs, where carbon dioxide is thrown off and oxygen taken on.

The pulmonary veins are four in number, two passing from the root of each lung to the posterior surface of the left auricle of the heart. Each vein is formed at the root of the lung by the union of a number of smaller vessels which take origin ultimately from the capillary net work formed from the branches of the pulmonary artery, and to a certain extent from that formed by the bronchial arteries. Each pulmonary vein is about six inches in length.

=The Coronary Circulation.=—The heart receives its blood supply through the two coronary arteries which arise from the aorta immediately above its origin, the return flow being by the coronary veins which open into the right auricle of the heart by the coronary sinus. The branches of the coronary arteries upon the surface of the heart are, as a rule, all end arteries; that is, arteries which form no direct anastomosis with their neighbors. Practically no blood can be carried directly, therefore, by the left coronary artery into the territory supplied by the right one, or vice versa.

The coronary sinus is a short venous trunk a little over an inch in length, which occupies the right half of that portion of the auriclo-ventricular groove which lies between the left auricle and ventricle. At the right end it opens into the right auricle, its orifice being guarded by the Thebesian valve.

=The Portal Circulation.=—This circulation is of little or no value to the embalmer, as no part of it is directly required to supply any of the tissues with embalming fluid.

The portal circulation is formed by the superior mesenteric vein and the splenic vein uniting to form the portal vein. The inferior mesenteric vein runs into the splenic vein; the gastric and cystic veins run into the portal veins. The portal vein ends in capillaries in the liver, where certain important changes take place, namely, the taking out of the bile.

The portal vein and its tributaries are unlike the veins in the general circulation, as there are no valves. Their function in life is to gather up food or nutrition for the blood, and to the embalmer is of no special importance, only to know how this circulation is made up. The vessels that convey blood to the liver in life and the fluid in death are discussed under the liver.

After death, about one-fourth of the blood of the body is to be found in the portal system. This blood can in no way be removed, and this is one of the reasons why the embalmer is not able to draw more blood than he does.

=The Foetal Circulation.=—The foetal circulation is that circulation existing between mother and unborn child.

_The placenta_ constitutes, from the third month of intra uterine life, the nutritive and respiratory organ of the foetus. The placenta consists of a maternal portion and a foetal portion. _The maternal portion_ is that portion of the placenta next to the uterine wall of the mother. In this are intervillus blood spaces, which may be regarded as derivations from the eroded maternal blood vessels. In the non-pregnant state the uterus is supplied with branches from the internal iliac artery, which end in capillaries in the wall of the uterus. In the pregnant state the numerous branches of the arteries supplying the uterus do not end as capillaries, but pierce the basal plate of the placenta, where the arterial vessels lose their muscular coat and open directly into the intervillus or intraplacental blood spaces. Maternal capillaries are wanting within the placenta, since they become early replaced by the intervillus spaces. The maternal blood is carried away from these spaces by wide venous channels, forming networks from which proceed the larger venous trunks.

_The foetal portion_ of the placenta is that portion next to the child. Here end the terminal loops of the foetal blood vessels, the blood being conveyed to and from the placenta along the umbilical cord, by the umbilical arteries and vein. Although coming into close relation, the blood streams of the mother and of the child never actually mingle, because of the delicate septum which intervenes. The delicate septum, however, allows the free interchange of gases necessary for the respiratory function as well as the passage of nutritive substances into the foetal circulation.

_The umbilical cord_ connects the body of the foetus with the placenta, and conveys the foetal blood to and from the placenta to the child. This blood is carried by means of two umbilical arteries and one umbilical vein.

The umbilical vein originates by means of capillaries in the placenta, traverses the cord and enters the body of the child at the umbilicus. The umbilical vein now enters the substance of the liver and passes from that organ to the ascending vena cava by means of the ductus venosus. The blood now enters the right auricle of the heart and the eustachian valve is so placed that this blood is thrown directly into the left auricle of the heart, from there into the left ventricle, and out into the aorta to find itself in the general circulation of the child. The blood coming from the upper extremities of the child finds its way into the right auricle of the heart by means of the descending vena cava, thence into the right ventricle, and out into the pulmonary artery. This artery after birth will lead the blood to the lungs, but before birth, in as much as the lungs are not functioning, the lungs can not accommodate this amount of blood, so it passes directly into the arch of the aorta by means of the ductus arteriosus, and thence into the general circulation. The umbilical or hypogastric arteries leave the internal iliacs, pass one on each side of the bladder to the umbilicus, and thence down the cord to the placenta, end there in capillaries, where the blood is now purified, and nourished for its return flow.

=The Collateral Circulation.=—By collateral circulation is meant the anastomoses of arteries, or veins through a side branch. There are three great arterial collateral circulations in the body. One is in the arm, the deep brachial artery, and the anastomotica magna, coming off of the brachial artery and anastomosing with the recurrent radial and ulnar artery. One is in the leg, the deep femoral artery, and the anastomotica magna coming off of the femoral artery and anastomosing with the recurrent anterior and posterior tibial arteries. One over the front part of the body, the superior and inferior mammary arteries branches of the subclavian artery and anastomosing with the superior and inferior epigastric arteries, branches of the external iliac and femoral arteries.

=The Lymphatic Circulation.=—The lymphatic system is a system of vessels which occurs abundantly in almost all portions of the body and converge and anastomose to form two or more main trunks, which open into the subclavian veins just before they are joined by the internal jugular. The vessels contain a fluid termed lymph, usually colorless and containing numerous white blood corpuscles known as lymphocytes.

In those vessels which have their origin in the wall of the small intestines, the contained fluid has, especially during digestion, a more or less milky appearance, owing to the lymphocytes being loaded with particles of fat which they have taken up from the intestinal contents. On this account, these vessels are usually spoken of as lacteals, although it must be recognized that they are merely portions of the general lymphatic system.

In certain respects the vessels of the system strongly resemble the veins. They arise from a capillary network, their walls have a structure closely resembling that of the veins, they are abundantly supplied with valves, and it may be said that the fluid which they contain flows from the tissues towards the subclavian veins. With these similarities there are combined marked differences. One of the most important of these consists in the fact that the capillaries of the lymphatics are closed and do not communicate with any other set of vessels as the venous capillaries do with the arterial; and another important difference is to be found in the frequent occurrence upon the lymphatic vessels of characteristic enlargements, the so-called lymphatic nodes or glands, quite different from anything occurring in connection with the veins.

Throughout the body spaces of varying size are found, containing a clear, more or less watery fluid, which are called lymph spaces. These spaces do not communicate with the capillaries of the lymphatics, but are in such close relationship with them that the fluid easily finds its way into the lymph capillaries by osmosis, absorption, lymphocytes going out into these spaces and returning filled with the lymph fluid.

The lymphatic capillaries, which are arranged in the form of networks of very different degrees of fineness and complexity, closely resemble in structure the blood capillaries, their walls consisting of a single layer of endothelial cells. They differ from those of the blood vascular system not only in their ultimate branches being closed, but also in their general appearance. They are of greater caliber.

The lymph vessels, which issue from the capillary networks and convey the lymph ultimately to the subclavian veins, have the arrangement closely resembling that of the veins; the larger ones are usually situated alongside and accompany the course of the blood vessels. Just as the veins unite to form larger trunks as they pass from the capillaries toward their termination, so, too, the lymphatics, but the lymphatics present two peculiarities which distinguish them from the veins. They do not anastomose as abundantly as veins and there is not the same proportional increase in the size of the lymphatic vessel. The left trunk or thoracic duct is much larger than the right, beginning in the abdominal region and traversing the entire length of the thorax to reach its destination. It receives all the lymph returned from the lower limbs, the pelvic walls and viscera, the abdominal walls and viscera, the lower part of the right half and the whole of the left half of the thoracic viscera, the left side of the neck and head, and the left arm. The other trunk, the right lymphatic duct, is very short and sometimes wanting. It receives the lymph from the upper part of the right side of the thoracic wall, from the right half of the thoracic viscera and the upper surface of the liver, the right side of the neck and head, and from the right arm. The structure of the larger lymphatic vessels is similar to the veins, but, as a rule, their walls are thinner than those of the veins of corresponding caliber and their valves are more numerous. The walls of the most robust trunks, particularly those of the thoracic duct, consist of three coats. From within outward these are: (a) the intima, composed of the endothelial lining and the fibro-subendothelial layer; (b) the media, made up of involuntary muscle interspersed with fibro-elastic tissue; and (c) the adventitia, consisting of fibro-elastic tissue and longitudinal bundles of involuntary muscle.

Lymphatic nodes are scattered along the course of the lymphatic vessels, found in various regions of the body as elliptical flattened nodules of varying size. The embalmer will meet with these in the axillary and inguinal regions, or when he is raising the axillary or femoral arteries.