101. The ribs successively and considera_The Philosophy of Health; Volume 1 (of 2) or, an exposition of the physical and mental constitution of man

as the seventh, by which the cavity they encompass is enlarged; from

the seventh they successively diminish in length, and the capacity of

the corresponding part of the cavity is lessened. The direction of the

ribs from above downwards is oblique (fig. XLV. 7, 8). Their external

or anterior surface is convex (fig. XLV. 7, 8); their internal or

posterior surface is concave: by the first their strength is increased;

by the second the general cavity of the thorax is enlarged (fig. XLV.

7, 8). Their upper margin is smooth and rounded, and gives attachment

to a double layer of muscles, called the intercostal, placed in the

intervals that separate the ribs from each other (fig. LIX.). Along

the lower margin is excavated a deep groove, for the lodgment and

protection of the intercostal vessels.

102. The ribs are connected with the spinal column chiefly by what is

termed the _anterior ligament_ (fig. LVI. 1), which is attached to the

head of the rib (fig. LVI.), and which, dividing into three portions

(fig. LVI. 1), firmly unites every rib to two of the vertebræ, and

to the intervertebral substance (fig. LVI. 1). This articulation is

fortified by a second ligament (fig. LVI. 2), also attached to a head

of the rib, termed the _interarticular_ (fig. LVI. 2), and by three

others, one of which is attached on the fore part, and the two others

in the back part, to the neck of the rib (fig. LVII. 1).

[Illustration: Fig. LVI.

Ligaments connecting the ribs to the spinal column. 1. anterior

ligaments; 2. interarticular ligament; 3. ligaments of the necks of the

ribs.]

The cartilages of the seven superior ribs are attached to the sternum

by a double layer of ligamentous fibres, termed the _anterior and the

posterior ligaments of the sternum_ (fig. LVIII.). So strong are the

bands which thus attach the ribs to the spinal column and the sternum,

that the ribs cannot be dislocated without fracture. "Such at least is

the case in experiments upon the dead body, where, though the rib be

subjected to the application of force by means of an instrument best

calculated to detach its head from the articulation, yet it is always

broken."

[Illustration: Fig. LVII.

1, &c. Ligaments connecting the ribs to the vertebræ behind.]

While thus firmly attached to their points of support, the ligaments,

which fix them, are so disposed as to render the ribs capable of being

readily moved upwards and downwards: upwards in inspiration; downwards

in expiration; and it is by this alternate action that they enlarge and

diminish the cavity of the thorax in the function of respiration.

[Illustration: Fig. LVIII.

Ligaments joining the cartilages of the ribs to the sternum.]

103. Such are the boundaries of the cavity of the thorax as far as

its walls are solid. The interspaces between these solid portions at

the sides are filled up by muscles, principally by those termed the

intercostal (fig. LIX.); below, the boundary is formed by the diaphragm

(fig. LXI. 2); while above, as has been already stated (69), the cavity

is so contracted as only to leave an opening for the passage of certain

parts to and from the chest.

[Illustration: Fig. LIX.

A view of the muscles called _Intercostals_, filling up the spaces

between the ribs.]

104. The inner surface of the walls of the thorax, in its whole

extent, is lined by a serous membrane, exceedingly thin and delicate,

but still firm, called the pleura. The same membrane is reflected over

the organs of respiration contained in the cavity, so as to give them

an external coat. The membrane itself is every where continuous, and

every where the same, whether it line the containing or the contained

parts; but it receives a different name as it covers the one or the

other: that portion of it which lines the walls of the cavity being

called the costal pleura (fig. LXI. _a_), while that which covers the

organs contained in the cavity is termed the pulmonary pleura (fig. LX.

5, 1).

105. A fold of each pleura passes directly across the central part

of the cavity of the thorax; extending from the spinal column to the

sternum, and dividing the general cavity into two. This portion of the

pleura is called the mediastinum, from its situation in the centre

of the thorax, and it so completely divides the thoracic cavity into

two, that the organs on one side of the chest have no communication

with those of the other; so that there may be extensive disease in one

cavity (for example, a large accumulation of water,) while the other

may be perfectly sound.

106. The main organs contained in the cavity of the thorax are the

lungs with their air tube; the heart with its great vessels; and the

tube passing from the mouth to the stomach (fig. LX.).

107. The two lungs occupy the sides of the chest (fig. LX. 5). They

are completely separated from each other by the membranous partition

just described, the mediastinum. Between the two folds of the

mediastinum, namely, in the middle of the chest, but inclining somewhat

to the left side, is placed the heart, enveloped in another serous

membrane, the pericardium (fig. LX. 2, 1).

108. The lungs are moulded to the cavities they fill; whence their

figure is conical, the base of the cone being downwards, resting on the

diaphragm (fig. LX. 5, _b_); and the apex upwards, towards the neck

(fig. LX. 5).

109. That surface of each lung which corresponds to the walls of the

chest is convex in its whole extent (fig. LX. 5); on the contrary, that

surface which corresponds to the mediastinum is flattened (fig. LX.

5). The basis of the lung is concave, adapted to the convexity of the

diaphragm on which it rests (fig. LX. 5).

110. The air-vessel of the lungs, termed the bronchus, together with

the blood-vessels and nerves, enter the organ at its flattened side,

not exactly in the middle, but rather towards the upper and back part.

This portion is termed the root of the lung.

111. The lungs are attached to the neck by the trachea (fig. LX. 4),

the continuation of which forms the bronchus; to the spinal column by

the pleura, and to the heart by the pulmonary vessels (fig. LX. 3,

_d_): their remaining portion is free and unattached.

112. In the living body, the lungs on each side completely fill the

cavity of the chest, following passively the movements of its walls,

and accurately adapting themselves to its size, whether its capacity

enlarge in inspiration, or diminish in expiration, so that the external

surface of the lung (the pulmonary pleura) is always in immediate

contact with the lining membrane of the walls of the cavity (the costal

pleura); consequently, during life, there is no cavity, the chest being

always completely full.

[Illustration: Fig. LX.

_a._ The cut edges of the ribs, forming the lateral boundaries of the

cavity of the thorax.

_b._ The diaphragm, forming the inferior boundary of the thorax, and

the division between the thorax and the abdomen.

_c._ The cut edges of the abdominal muscles, turned aside, exposing the

general cavity of the abdomen.

1. The cut edge of the pericardium turned aside.

2. The heart.

3. The great vessels in immediate connexion with the heart.

4. The trachea, or wind-pipe.

5. The lungs.

6. The liver.

7. The stomach.

8. The large intestine.

9. The small intestines.

10. The urinary bladder.]

113. The anterior surface of the pericardium, the bag which envelopes

the heart, lies immediately behind the sternum, and the cartilages of

the second, third, fourth, and fifth ribs, covered at its sides by the

pleura, and firmly attached below to the diaphragm (fig. LX. 1).

114. Surrounded by its pericardium, within the mediastinum, the heart

is placed nearly in the centre of the chest, but its direction is

somewhat oblique, its apex being directly opposite to the interval

between the fifth and sixth ribs on the left side (fig. LX. 2); while

its basis is directed upwards, backwards, and towards the right (fig.

LX. 2). That portion of its surface which is presented to view on

opening the pericardium is convex (fig. LX. 2); but its opposite

surface, namely, that which rests upon the part of the pericardium

which is attached to the diaphragm, is flattened (fig. LX. 1). It is

fixed in its situation partly by the pericardium and partly by the

great vessels that go to and from it. But under the different states

of expiration and inspiration, it accompanies, in some degree, the

movements of the diaphragm; and in the varied postures of the body,

the heart deviates to a certain extent from the exact position here

described.

115. The second division of the trunk, the _abdomen_, is bounded above

by the diaphragm (fig. LXI. 2), below by the pelvis (fig. LXI. 3),

behind and at the sides by the vertebræ and muscles of the loins (fig.

LXIII.), and before by the abdominal muscles (fig. LXIII. 9).

116. The organ which forms the superior boundary of the abdomen, the

diaphragm (midriff), is a circular muscle, placed transversely across

the trunk, nearly at its centre (fig. LXI. 2). It forms a vaulted

partition between the thorax and the abdomen (fig. LXI. 2). All around

its border it is fleshy (fig. LXI. 2); towards its centre it is

tendinous (fig. LXI. 2); the surface towards the abdomen is concave

(fig. LXI. 2); that towards the thorax convex (fig. LXI. 2); while its

middle tendinous portion ascends into the thorax as high as the fourth

rib (fig. LXI. 2).

[Illustration: Fig. LXI.

View of the diaphragm. 1. Cavity of the thorax; 2. diaphragm separating

the cavity of the thorax from that of the abdomen; 3. cavity of the

pelvis.]

117. The diaphragm is perforated by several apertures, for the

transmission of tubes and vessels, which pass reciprocally between the

thorax and abdomen (fig. LXII.).

1. A separate aperture is formed to afford an exit from the thorax

of the aorta, the common source of the arteries (fig. LXII. 2), and

an entrance into the thorax of the thoracic duct, the tube that bears

the digested aliment to the heart. 2. A little to the left of the

former, there is another aperture, through which passes the esophagus

or gullet (fig. LXII. 3), the tube that conveys the food from the mouth

to the stomach. 3. On the right side, in the tendinous portion of the

diaphragm, very carefully constructed, is a third aperture for the

passage of the vena cava (fig. LXII. 4), the great vessel that returns

the blood to the heart from the lower parts of the body.

[Illustration: Fig. LXII.

View of the diaphragm with the tubes that pass through it. 1. Arch

of the diaphragm; 2. the trunk of the aorta passing from the chest

into the abdomen; 3. the esophagus passing from the chest through the

diaphragm to the stomach; 4. the vena cava, the great vein that returns

the blood to the heart from the lower parts of the body, passing from

the abdomen, into the chest, in its way to the right side of the heart;

5. 6. muscles that arise in the interior of the trunk and that act upon

the thigh; 5. the muscle called psoas; 6. the muscle called iliacus.]

118. The partition formed by the diaphragm between the thorax and

abdomen, though complete, is moveable; for as the diaphragm descends in

inspiration and ascends in expiration, it proportionally enlarges or

diminishes the cavities between which it is placed; consequently, the

actual magnitude of these cavities varies every moment, and the size of

the one is always in the inverse ratio of that of the other.

119. Between the abdomen and the pelvis there is no separation; one

cavity is directly continuous with the other (fig. LXI. 3); but along

the inner surface of the expanded bones, which form a part of the

lateral boundary of the abdomen, there is a prominent line, termed

the brim of the pelvis (fig. XLV. 15), marking the point at which the

abdomen is supposed to terminate and the pelvis to commence.

120. Behind and at the sides the walls of the abdomen are completed

partly by the lumbar portion of the spinal column and partly by the

lumbar muscles (fig. XLV. 4), and before by the abdominal muscles (fig.

LXIII. 9).

121. The inner surface of the walls of the abdomen is lined throughout

by a serous membrane, termed the peritoneum (fig. LXIII.). From the

walls of the abdomen, the peritoneum is reflected upon the organs

contained in the cavity, and is continued over them so as to form their

external coat. The peritoneum also descends between the several organs,

connecting them together, and holding them firmly in their situation;

and it likewise forms numerous folds, in which are embedded the vessels

and nerves that supply the organs. It secretes a serous fluid, by

which its own surface and that of the organs it covers is rendered

moist, polished, and glistening, and by means of which the organs

glide smoothly over it, and over one another in the various movements

of the body, and are in constant contact without growing together. In

structure, distribution, and function, the peritoneum is thus perfectly

analogous to the pleura.

122. Like the thorax, the abdomen is always completely full. When

the diaphragm is in action, it contracts. When the diaphragm is

in the state of contraction, the abdominal and lumbar muscles are

in the state of relaxation. By the contraction of the diaphragm,

the organs contained in the abdomen are pushed downwards, and the

anterior and lateral walls of the cavity being at this moment in

a state of relaxation, they readily yield, and, consequently, the

viscera are protruded forwards and at the sides. But the abdominal

and lumbar muscles in their turn contract, the diaphragm relaxing;

and, consequently, the viscera, forced from the front and sides of the

abdomen, are pushed upwards, together with the diaphragm, into the

cavity of the thorax. A firm and uniform pressure is thus at all times

maintained upon the whole contents of the abdomen: there is an exact

adaptation of the containing to the contained parts, and of one organ

to another. No space intervenes either between the walls of the abdomen

and the organs they enclose, or between one organ and another: so that

the term cavity does not denote a void or empty space, but merely the

extent of the boundary within which the viscera are contained.

123. The contents of the abdomen consist of the organs which belong to

the apparatus of digestion, and of those which belong to the apparatus

of excretion.

124. The organs which belong to the apparatus of digestion are—1. The

stomach (fig. LXIII. 2) 2. The duodenum (fig. LXIII. 4). 3. The jejunum

(fig. LXIII. 5). 4. The ilium (fig. LXIII. 5). The three last organs

are called the small intestines, and their office is partly to carry on

the digestion of the aliment commenced in the stomach, and partly to

afford an extended surface for the absorption of the nutriment as it is

prepared from the aliment. 5. The pancreas (fig. LXIV. 5). 6. The liver

(fig. LXIV. 2). 7. The spleen (fig. LXIV. 4). The three last organs

truly belong to the apparatus of digestion, and their office is to

co-operate with the stomach and the small intestines in the conversion

of the aliment into nutriment.

[Illustration: Fig. LXIII.

1. Esophagus; 2. stomach; 3. liver raised, showing its under surface;

4. duodenum; 5. small intestines; 6. cæcum; 7. colon; 8. urinary

bladder; 9. gall bladder; 10. abdominal muscles divided and reflected.]

125. The organs which belong to the apparatus of excretion are—1. The

large intestines consisting of the cæcum (fig. LXIII. 6). 2. The colon

(fig. LXIII. 7). 3. The rectum (fig. LXIV. 10). It is the office of

these organs, which are called the large intestines, to carry out of

the system that portion of the alimentary mass which is not converted

into nourishment. 4. The kidneys (fig. LXIV. 6), the organs which

separate in the form of the urine an excrementitious matter from the

blood, in order that it may be conveyed out of the system.

[Illustration: Fig. LXIV.

General view of the viscera of the abdomen. 1. Stomach raised; 2. under

surface of liver; 3. gall bladder; 4. spleen; 5. pancreas; 6. kidneys;

7. ureters; 8. urinary bladder; 9. portion of the intestine called

duodenum; 10. portion of the intestine called rectum; 11. the aorta.]

126. The last division of the trunk, called the pelvis (fig. LXI. 3),

consists of a circle of large and firm bones, interposed between the

lower portion of the trunk and the inferior extremities (fig. XLV.).

The bones that compose the circle, distinct in the child, are firmly

united in the adult into a single piece; but as the original separation

between each remains manifest, they are always described as separate

bones. They are the sacrum (fig. XLV. 5), the coccyx (fig. XXXV.), the

ilium (fig. XLV. 11), the ischium (fig. XLV. 12), and the pubis (fig.

XLV. 13).

127. The sacrum, placed like a wedge between the moveable portion

of the spinal column and the lower extremities, forms the posterior

boundary of the pelvis. The figure of this bone is triangular (fig.

XLV. 5); its anterior surface is concave and smooth, for enlarging the

cavity of the pelvis and sustaining the organs contained in it (fig.

XLV. 5); its posterior surface is convex, irregular, and rough (fig.

XXXV.), giving origin to the great muscles that form the contour of the

hip, and to the strong muscles of the back and loins that raise the

spine and maintain the trunk of the body erect.

128. The base or upper part of the sacrum receives the last vertebra

of the loins on a large and broad surface (fig. XLV. 4), forming a

moveable joint; and the degree of motion at this point is greater than

it is at the higher points of the spinal column. Firmly united at its

sides with the haunch bones, it admits there of no degree of motion.

129. The coccyx, so named from its resemblance to the beak of the

cuckoo, when elongated by a succession of additional bones, forms the

tail in quadrupeds; but in man it is turned inwards to support the

parts contained in the pelvis, and to contract the lower opening of

the cavity. By means of a layer of cartilage, the medium by which this

bone is connected with the sacrum, it forms a moveable articulation,

continuing moveable in men until the age of twenty-five, and in women

until the age of forty-five; continuing moveable in women thus long, in

order that by yielding to the force which tends to push it backwards

during the period of labour, it may enlarge the lower aperture of the

pelvis, and so facilitate the process of parturition and diminish its

suffering.

130. The lateral boundaries of the pelvis are formed by the ilium,

the haunch bone (fig. XLV. 11), and by the ischium, the hip bone (fig.

XLV. 12). The ilium forms the lower part of the abdomen and the upper

part of the pelvis (fig. XLV. 11); its broad expanded wing supports the

contents of the abdomen, and gives attachment to the muscles that form

the anterior portion of its walls (figs. XLV. 11, and LXIII. 9); its

external convex surface sustains the powerful muscles that extend the

thigh; and along its internal surface is the prominent line which marks

the brim of the pelvis (fig. XLV. 15), and which divides this cavity

from that of the abdomen.

131. The ischium or hip bone is the lower part of the pelvis (fig.

XLV. 12); at its undermost portion is a rounded prominence called

the tuberosity (fig. XLV. 12), in its natural condition covered with

cartilage, upon which is superimposed a cushion of fat. It is this part

on which the body is supported in a sitting posture.

132. The pubis or share bone forms the upper and fore part of the

pelvis (fig. XLV. 13), and together with the two former bones,

completes the large and deep socket, termed the acetabulum (fig. XLV.

14), into which is received the head of the thigh-bone (fig. XXXIV.

4). The margin of the acetabulum and the greater part of its internal

surface is lined with cartilage, so that in its natural condition it is

much deeper than it appears to be when the bones alone remain.

133. The lower aperture of the pelvis, which appears large when all

the soft parts are removed, is not really large, for in its natural

state it is filled up partly by muscles and partly by ligaments, which

sustain and protect the pelvic organs, leaving only just space enough

for the passage to and from those which have their opening on the

external surface.

134. The cavity of the pelvis, together with all the organs contained

in it, are lined by a continuation of the membrane that invests the

abdomen and its contents.

135. The organs contained in the pelvis are the rectum (fig. LXIV. 9),

which is merely the termination of the large intestines, the urinary

bladder (fig. LXIV. 8), and the internal part of the apparatus of

reproduction.

136. The large and strong bones of the pelvis not only afford lodgment

and protection to the tender organs contained in its cavity, but

sustain the entire weight of the body, the trunk resting on the sacrum

as on a solid basis (fig. XLV. 5), and the lower extremities being

supported in the sockets in which the heads of the thigh-bones play, in

the varied movements of locomotion (fig. XXXIV. 4).

137. The last division of the body comprehends the superior and the

inferior extremities.

138. The superior extremities consist of the shoulder, arm, fore-arm,

and hand.

139. The soft parts of the SHOULDER are composed chiefly of muscles;

its bones are two, the scapula or the _blade bone_, and the clavicle or

the _collar bone_ (fig. LXV. 2, 4).

[Illustration: Fig. LXV.

1. Sternum; 2. clavicle; 3. ribs; 4. anterior surface of scapula; 5.

coracoid process of scapula; 6. acromion process of scapula; 7. margin

of glenoid cavity of scapula; 8. body of the humerus or bone of the

arm; 9. head of the humerus.]

140. The SCAPULA is placed upon the upper and back part of the thorax,

and occupies the space from the second to the seventh ribs (fig. LXV. 4)

[Illustration: Fig. LXVI.

1. Posterior surface of scapula; 2. margin of scapula; 3. acromion

process; 4. margin of glenoid cavity; 5. clavicle; 6. body of humerus;

7. head of humerus.]

Unlike that of any other bone of the body, it is embedded in muscles,

without being attached to any bone of the trunk, excepting at a single

point. From the bones of the thorax it is separated by a double layer

of muscles, on which it is placed as upon a cushion, and over the

smooth surface of which it glides. Originally, like the bones of the

skull, it consisted of two tables of compact bone, with an intermediate

layer of spongy bony substance (diploë); but, by the pressure of the

muscles that act upon it, it gradually grows thinner and thinner,

until, as age advances, it becomes in some parts quite transparent and

as thin as a sheet of paper.

141. The figure of the scapula is that of an irregular triangle (fig.

LXVI.). Its anterior surface is concave (fig. LXV. 4), corresponding to

the convexity of the ribs (fig. XLV. 7); its posterior surface is very

irregular (fig. LXVI. 1), being in some parts concave and in others

convex, giving origin especially to two large processes (figs. LXV. 5,

and LXVI. 3); one of which is termed the _acromion_ (fig. LXVI. 3),

and the other the _coracoid_ process of the scapula (fig. LXV. 5). The

margins of the bone, whatever the thinness of some portions of it, are

always comparatively thick and strong (fig. LXVI. 2), affording points

of origin or of insertion to powerful muscles. At what is called the

anterior angle of the bone there is a shallow oval depression covered

with cartilage and deepened by a cartilaginous margin, called the

_glenoid_ cavity of the scapula (figs. LXV. 7, and LXVI. 4), which

receives the head of the humerus or bone of the arm (figs. LXV. 9, and

LXVI. 7, 6).

142. The clavicle, the second bone of the shoulder, is a long and

slender bone, of the form of an italic [Illustration], projecting

a little forwards towards its middle, so as to give a slight convexity

of outline to the top of the chest and the bottom of the neck (fig.

LXV. 2). It is attached by one extremity to the sternum (fig. LXV. 2)

and by the other to the scapula (fig. LXV. 2), by moveable joints. The

nature of an immoveable joint has been explained (63). In the connexion

of the bones of the trunk, while the main object is to secure firmness

of attachment, some degree of motion is at the same time obtained (81

et seq.): but the mode in which the several bones of the extremities

are connected with each other and with the trunk, admits of so great a

degree of motion, that these articulations are pre-eminently entitled

to the name of moveable joints. The component parts of all moveable

joints are bone, cartilage, synovial membrane, and ligament. The great

character of a moveable joint is the approximation of two or more

bones; yet these bony surfaces are never in actual contact, but are

invariably separated from each other by cartilage. The cartilage either

covers the entire extent of the articulating surface of the bones,

as in the shoulder-joint, where both the head of the humerus and the

cavity of the scapula that receives it are enveloped in this substance

(fig. LXV. 7. 9), or a portion of it is placed between the articulating

surfaces of the bones, as in the joint between the clavicle and sternum

(fig. LXVII. _a_); which, when so placed, is termed an interarticular

cartilage (fig. LXVII. _a_). By its smooth surface cartilage lessens

friction; while by its elasticity it facilitates motion and prevents

concussion. Slightly organized cartilage is provided with comparatively

few blood-vessels and nerves. Had it been vascular and sensible like

the skin and the muscle, the force applied in the movements of the

joint would have stimulated the blood-vessels to inordinate action, and

the sensibility of the nerves would have been the source of constant

pain: every motion of every joint would have been productive of

suffering, and have laid the foundation of disease. The facility and

ease of motion obtained by the smoothness, elasticity, and comparative

insensibility of cartilage are still further promoted by the fluid

which lubricates it, termed synovia, secreted by a membrane called

synovial, which lines the internal surface of the joint, and which

bears a close resemblance to the serous (30). Synovia is a viscid

fluid of the consistence of albumen (5). It is to the joint what oil

is to the wheel, preventing abrasion and facilitating motion; but it

is formed by the joint itself, at the moment when needed, and in the

quantity required. The motion of the joint stimulates the synovial

membrane to secretion, and hence the greater the degree of motion, the

larger the quantity of lubricating fluid that is supplied. The several

parts of the apparatus of moveable joints are retained in their proper

position by ligamentous substance, which, as has been shown (96 and

97), is oftentimes so strong that it is easier to fracture the bone

than to tear the ligament, and in every case the kind and extent of

motion possessed by the joint are dependent mainly on the form of

the articulatory surfaces of the bones and on the disposition of the

ligaments.

143. In the joint formed by the clavicle and the sternum (fig. LXVII.

_a_) an interarticular cartilage is placed between the two bones which

are united, first by a strong fibrous ligament, which envelops them

as in a capsule (fig. LXVII. 1); by a second ligament, which extends

from the cartilage of the first rib to the clavicle (fig. LXVII. 4),

by which the attachment of the clavicle to the sternum is materially

strengthened; and by a third ligament which passes transversely from

the head of one clavicle to that of the other (fig. LXVII. 3). The

joint thus formed, though so strong and firm that the dislocation of

it is exceedingly rare, yet admits of some degree of motion in every

direction, upwards, downwards, forwards, and backwards; and this

articulation is the sole point by which the scapula is connected with

the trunk, and consequently by which the upper extremity can act, or be

acted upon, by the rest of the body.

[Illustration: Fig. LXVII.

1. The fibrous capsule of the sternum and clavicle; 2. the same laid

open, showing _a_, the interarticular cartilage; 3. the ligament

connecting the two clavicles; 4. the ligament joining the clavicle to

the first rib; 5. ligaments passing down in front of the sternum.]

144. The scapular extremity of the clavicle (fig. LXVIII. 6) is

attached to the processes of the scapula (fig. LXVIII. 4. 3) by several

ligaments of great strength (fig. LXVIII. 7, 8, 9). First by very

strong fasciculi which pass from the upper surface of the clavicle

to the acromion of the scapula (fig. LXVIII. 6); and secondly by two

ligaments which unite the clavicle with the coracoid process of the

scapula (fig. LXVIII. 8, 9). These ligaments are so powerful that they

resist a force capable of fracturing the clavicle; and they need to be

thus strong, for the clavicle is a shaft which sustains the scapula,

and through the scapula the whole of the upper extremity; and the main

object of the joint by which these bones are united, is to afford a

firm attachment of the scapula to its point of support.

[Illustration: Fig. LXVIII.

1. The clavicle; 2. the anterior part of the scapula; 3. the coracoid

process; 4. the acromion process; 5. the humerus; 6. ligaments binding

the scapular end of the clavicle to the acromion; 7. 8. 9. ligaments

passing from one process of the scapula to the other; 10. the fibrous

capsule of the shoulder-joint.]

145. The clavicle serves the following uses: it sustains the upper

extremity; it connects the upper extremity with the thorax; it prevents

the upper extremity from falling forwards upon the thorax; and it

affords a fixed point for steadying the extremity in the performance of

its various actions.

146. The glenoid cavity of the scapula (fig. LXV. 7) receives the head

of the humerus, the bone of the arm (fig. LXV. 9), and the two bones

being united by ligament form the shoulder-joint (fig. LXVIII.). This

joint is what is termed a ball and socket joint, the peculiarities

of which are two: first, beyond all others this mode of articulation

admits of free and extensive motion; in the present case, there is

the utmost freedom of motion in every direction, upwards, downwards,

backwards, and forwards. In the second place, this mode of articulation

admits of the motion of the limb without that of the body, or of the

motion of the body without that of the limb. When at rest, the arm may

be moved in almost any direction without disturbing the position of any

other part of the frame; the manifold advantages of which are obvious.

On the other hand, by careful management, very considerable variations

in the posture of the body may be effected without the communication

of any degree of motion to the limb; an unspeakable advantage when the

limb has sustained injury, or is suffering from disease.

147. It does not seem possible to construct a joint of great strength,

capable, at the same time, of the degree of motion possessed by the

joint of the shoulder. So shallow is the socket of the scapula, and

so large the head of the humerus, that it seems as if the slightest

movement must dislodge it from its cavity (fig. LXVI. 4. 7). For

sustaining heavy weights or resisting a great amount of pressure,

applied to it suddenly and in various directions, the arm is obviously

unfitted. But this is not its office. The superior extremities are the

organs of apprehension—the instruments by which the mind executes

the commands of the will. They do not need the strength required by

the organs that sustain the weight of the body and that perform the

function of locomotion; but they do need freedom and extent of motion:

to this strength may be sacrificed, and so it is; yet what can be

done to combine strength with mobility is effected. Large and strong

processes of bone, proceeding as has been shown (141), from the convex

surface of the scapula (figs. LXV. and LXVI.), overhang, and to a

considerable extent surround, the head of the arm-bone, especially

resisting the force that would dislodge it from its socket and drive

it upwards, inwards, and backwards (fig. LXV.), the directions in

which force is most commonly applied to it. By these processes of bone

the joint is greatly strengthened, especially in those directions.

Moreover, a strong ligament, termed the fibrous capsule (fig. LXVIII.

10) envelops the joint. This ligament, arising from the neck of

the scapula (fig. LXVIII. 10), expands itself in such a manner as

completely to surround the head of the humerus (fig. LXVIII. 10); and

then again contracts in order to be inserted into the neck of the bone

(fig. LXVIII. 10). This ligament is strengthened by the tendons of no

less than four muscles which are expanded over it, as well as by the

powerful substance termed fascia which is reflected upon it from both

the processes and ligaments of the scapula. In addition to all these

expedients for fortifying the joint, it receives a further security

in the position of the scapula, which is loose and unattached; which

slides easily over the ribs upon its cushion of flesh; which thus

obtains, by its facility of yielding, some compensation for its want of

strength, eluding the force which it cannot resist.

148. The arm consists of numerous and powerful muscles, and of a

single bone, the humerus, which belongs to the class of bones termed

cylindrical (185).

149. The upper end of the humerus terminates in a circular head

(fig. LXV. 9), which is received into the socket of the scapula (fig.

LXV. 9. 7) termed, as has been stated (141), its glenoid cavity. The

middle portion of the bone, or what is termed its shaft (fig. LXV. 8),

diminishes considerably in magnitude, and becomes somewhat rounded

(fig. LXV. 8), while its lower end again enlarges, and is spread out

into a flattened surface of great extent (fig. LXIX. 1, 3, 2, 4). Of

this broad flattened surface, the middle portion is grooved (fig. LXIX.

2): it is covered with cartilage; it forms the articulating surface

by which the arm is connected with the fore-arm. On each side of this

groove there is a projection of bone or tubercle, termed condyle (fig.

LXIX. 3, 4), the inner (fig. LXIX. 3) being much larger than the outer

(fig. LXIX. 4). The inner condyle gives origin to the muscles that

bend, the outer to those that extend the fore-arm and the fingers

(figs. LXXXIV. 1, 2, and LXXXV. 1).

[Illustration: Fig. LXIX.

1. Lower extremity of the humerus; 2. grooved surface; 3. internal

condyle; 4. external condyle; 5. the upper part of the ulna; 6. the

head; 7. the neck; 8. the tubercle of the radius.]

150. The muscles that act upon the arm arise from the back (fig.

LXXII. 2), the chest (fig. LXXI. 1), the clavicle (fig. LXXI. 1), and

the scapula (fig. LXXI. 3); and they move the arm with freedom and

power upwards, downwards, forwards, backwards, inwards, and outwards.

The chief muscle that raises the arm is the deltoid (fig. LXXI. 3),

which arises partly from the clavicle and partly from the scapula

(fig. LXXI. 3). It has the appearance of three muscles proceeding in

different directions, the different portions being separated by slight

fissures (figs. LXXI. 3, and LXXII. 3). The fibres converging unite

and form a powerful muscle which covers the joint of the humerus (fig.

LXXI. 3). It is implanted by a short and strong tendon into the middle

of the humerus (fig. LXXI. 4). Its manifest action is to pull the arm

directly upwards. Its action is assisted by the muscles that cover

the back of the scapula, which are in like manner inserted into the

humerus, and which, at the same time that they elevate the arm, support

it when raised.

[Illustration: Fig. LXXI.

View of the muscles on the fore part of the chest that act upon the

arm. 1. The muscle called the great pectoral; 2. the small pectoral; 3.

the deltoid; 4. the humerus.]

151. The principal muscle that carries the arm downwards is the

latissimus dorsi (fig. LXXII. 2), the broadest muscle of the body,

which, after having covered all the lower part of the back and loins,

terminates in a thin but strong tendon which stretches to the arm, and

is implanted into the humerus (fig. LXXII. 2), near the tendon of a

muscle immediately to be described,—the great pectoral. When the arm

is raised by the deltoid and its assistant muscles, the latissimus

dorsi carries it downwards with force, and its powerful action is

increased by that of other muscles which arise from the scapula and are

inserted into the arm.

152. The principal muscle that carries the arm forwards towards the

chest, is the great pectoral (fig. LXXI. 1), which, arising partly from

the clavicle (fig. LXXI. 1), partly from the sternum (fig. LXXI. 1),

and partly from the cartilages of the second, third, fourth, fifth, and

sixth ribs (fig. LXXI. 1), covers the greater part of the breast (fig.

LXXI. 1). Its fibres, converging, terminate in a strong tendon, which

is inserted near the tendon of the longissimus dorsi into the humerus,

about four inches below its head (fig. LXXI. 1). These two muscles form

the axilla or armpit, the anterior border of the axilla consisting of

the pectoral muscle. Though each of these muscles has its own peculiar

office, yet they often act in concert, thereby greatly increasing their

power, and the result of their combined action is to carry the arm

either directly downwards or to the side of the chest.

[Illustration: Fig. LXXII.

View of the muscles seated on the back part of the trunk that act

upon the shoulder and arm. 1. The muscle called the trapezius; 2. the

latissimus dorsi; 3. the deltoid.]

153. Some of the muscles that elevate the arm carry it inwards, and

others outwards; the muscles that carry it forwards likewise carry it

inwards; while of the muscles that pull it downwards, some direct it

forwards and inwards, and others backwards and outwards (151 and 152).

154. It has been already stated that the shoulder-joint is completely

surrounded by the muscular fibres or the tendinous expansions of

several of these powerful muscles, which have a far greater effect in

maintaining the head of the humerus in its socket than the fibrous

capsule of the joint; the latter being necessarily loose, in order

to allow of the extended and varied motions of the arm, whereas the

muscles that encompass the joint adhere closely and firmly to it.

Moreover, by virtue of their vital power these muscles act with an

efficiency which a mere ligamentous band is incapable of exerting; for

they apportion the strength of resistance to the separating force, and

react with an energy proportioned to the violence applied.

155. The bones of the fore-arm are two, the ulna and the radius (figs.

LXIX. and LXXIII.). The ulna is essentially the bone of the elbow

(figs. LXIX. 5, and LXXIII. 3); the radius that of the hand (fig.

LXXV.). Supposing the arm to hang by the side of the body, and the palm

of the hand to be turned forwards, the ulna, in apposition with the

little finger, occupies the inner; and the radius, in apposition with

the thumb, occupies the outer part of the fore-arm (fig. XXXIV. 3).

[Illustration: Fig. LXXIII.

1. The internal condyle of the humerus; 2. the external

condyle of the humerus; 3. the olecranon process of the ulna;

4. the head of the radius.]

156. The upper end of the ulna belonging to the elbow is large (figs.

LXIX. 5, and LXXIII. 3). It sends backwards the large projection

commonly named the elbow or _olecranon_ (fig. LXXII. 3), in the centre

of which there is a smooth and somewhat triangular surface (fig.

LXXIII. 3) which is always covered by skin of a coarse texture, like

that placed over the lower part of the knee-pan, as if nature intended

this for a part on which we may occasionally lean and rest. Large at

the elbow, the ulna gradually grows smaller and smaller as it descends

towards the wrist, where it ends in a small round head (fig. LXXXII.

2), beyond which, on the inner side, or that corresponding to the

little finger, it projects downwards a small rounded point, termed

the styloid process (fig. LXXXII. 3). As the styloid process and the

olecranon, the two extremities of the ulna (figs. LXXIII. 3, and

LXXII. 3), are easily and distinctly felt, the length of this bone was

primitively used as a measure, called a cubit, which was the ancient

name of the bone.

157. The radius, the second bone of the fore-arm, placed along its

outer part next the thumb, is small at its upper end (figs. LXIX. 6,

and LXXIII. 4); but its body is larger than that of the ulna; while its

lower end, next the wrist to which it properly belongs, is very bulky

(fig. LXXXII. 1). Its upper end is formed into a small circular head,

which is united by distinct joints both to the humerus and to the ulna

(fig. LXIX. 6). The top of its rounded head is excavated into a shallow

cup (figs. LXIX. 6, and LXXIII. 4) which receives a corresponding

convexity of the humerus (fig. LXIX. 2), and its lower extremity is

excavated into an oblong cavity, which receives two of the bones of the

wrist (fig. LXXXIII. 1. 4).

158. The joint of the elbow is composed above of the condyles of the

humerus (fig. LXIX. 3. 2), and below by the heads of the ulna and

radius (fig. LXIX. 5. 6).

159. The upper surface of the ulna is so accurately adapted to the

lower surface of the humerus that the one seems to be moulded on

the other (figs. LXIX. 5, and LXXIII. 3), and the form of these

corresponding surfaces, which are everywhere covered with cartilage,

is such as to admit of free motion backwards and forwards, that is,

of extension and flexion; but to prevent any degree of motion in any

other direction. The joint is therefore a hinge-joint, of which the two

motions of flexion and extension are the proper motions. This hinge is

formed on the part of the humerus by a grooved surface, with lateral

projections (fig. LXIX. 2, 3, 4), and on the part of the ulna by a

middle projection with lateral depressions (fig. LXIX. 5): the middle

projection of the ulna turning readily on the grooved surface of the

humerus (fig. LXIX. 2).

160. The bones are held in their proper situation, first, by a

ligament on the fore part of the arm, called the anterior (fig. LXXIV.

6), which arises from the lower extremity of the humerus, and is

inserted into the upper part of the ulna and the coronary ligament of

the radius (fig. LXXIV. 6. 8); secondly, by another ligament on the

back part of the arm, called the posterior ligament (fig. LXXV. 8),

placed in the cavity of the humerus that receives the olecranon of the

ulna (fig. LXXV. 8); and thirdly, by two other ligaments at the sides

of the ulna (fig. LXXV. 6, 7). The ulna and radius are united, first,

by a ligament called the coronary, which, arising from the ulna, passes

completely around the head of the radius (fig. LXXVI. 3), and the

attachment of which, while sufficiently close to prevent the separation

of the two bones, is yet not adherent to the radius, for a reason

immediately to be assigned; secondly, by another ligament which passes

in an oblique direction from one bone to the other (fig. LXXVI. 4);

and thirdly, by a dense and broad ligament, termed the _interosseous_

(figs. LXXIV. 10, and LXXVI. 5), which fills up the space between the

two bones nearly in their whole extent. This ligament serves other

offices besides that of forming a bond of union, affording, more

especially, a greater extent of surface for the attachment of muscles,

and separating the muscles on the anterior from those on the posterior

part of the limb.

[Illustration: Fig. LXXIV.

Anterior view of the ligaments of the elbow-joint. 1. The

lower portion of the humerus; 2. the upper portion of the

radius; 3. the upper portion of the ulna; 4. the internal

condyle; 5. the external condyle; 6. the anterior ligament;

7. portion of the internal lateral ligament; 8. portion of

the coronary ligament; 9. the oblique ligament; 10. upper

portion of the interosseous ligament.]

[Illustration: Fig. LXXV.

Posterior view of the ligaments of the elbow-joint. 1. Lower

end of the humerus; 2. internal condyle; 3. external condyle;

4. the olecranon process of the ulna; 5. the upper portion of

the radius; 6. the internal lateral ligament; 7. the external

lateral ligament; 8. the posterior ligament.]

[Illustration: Fig. LXXVI.

View of the ligaments connecting the ulna and radius at their upper

part. 1. The radius; 2. the ulna; 3. the coronary ligament surrounding

the head of the radius; 4. the oblique ligament passing from the ulna

to the tubercle of the radius; 5 the upper portion of the interosseous

ligament.]

161. At their inferior extremities the ulna and radius are united

partly by the interosseous ligament (fig. LXXVII. 1) and partly by

ligamentous fibres which pass transversely from one bone to the other

(fig. LXXVII. 2) on the anterior and the posterior surface of the

fore-arm.

[Illustration: Fig. LXXVII.

1. Interosseous ligament; 2. transverse fibres passing between the

radius and ulna, and uniting the two bones; 3. 4. 5. posterior and

lateral ligaments of the wrist joint; 6. ligaments uniting the bones of

the wrist with one another; 7. 8. ligaments which attach the metacarpal

to the carpal bones; 9. transverse ligaments for the attachment of the

phalanges of the fingers; 10. lateral ligaments for the attachment of

the phalanges of the fingers 11. ligaments of the thumb.]

162. The lower extremity of the radius is also united to the wrist;

and the hand being attached to the wrist, the junction of the hand and

the fore-arm is effected by the articulation of the wrist with the

radius (fig. LXXVII.). The ligaments which connect the bones of the

wrist with the radius are bands of exceeding strength (fig. LXXVII. 3).

163. The muscles that act upon the fore-arm are placed upon the arm

(fig. LXXVIII.). The joint of the elbow being a hinge-joint, the

fore-arm can admit only of two motions, namely, flexion and extension.

The muscles by which these motions are effected are four, two for each;

the two flexors being placed on the fore part (fig. LXXVIII. 2. 4), and

the two extensors on the back part of the arm (fig. LXXIX. 5).

164. The two flexor muscles of the fore-arm are termed the biceps and

the brachialis (fig. LXXVIII. 2, 4). The biceps is so called because

it has two distinct heads or points of origin (fig. LXXVIII. 2), both

of which arise from the scapula (fig. LXXVIII. 2). About a third part

down the humerus the two heads meet, unite and form a bulky muscle

(fig. LXXVIII. 2), which, when it contracts, may be felt like a firm

ball on the fore part of the arm, the upper part of the ball marking

the point of union of the two heads (fig. LXXVIII. 2). The muscle

gradually becoming smaller, at length terminates in a rounded tendon

(fig. LXXVIII. 3), which is implanted into the tubercle of the radius

a little below its neck (fig. LXXVIII. 3). It is an exceedingly thick

and powerful muscle, and its manifest action is to bend the fore-arm

with great strength. But since its tendon is inserted into the radius,

besides bending the fore-arm, it assists other muscles that also act

upon the radius in the performance of a function to be described

immediately (168).

[Illustration: Fig. LXXVIII.

View of the flexor muscles of the fore-arm. 1. The anterior surface

of the scapula; 2. the muscle called biceps; 3. tendon of the biceps

passing to the tubercle of the radius; 4. the muscle called brachialis.]

165. The second flexor of the fore-arm, termed the brachialis, is

placed immediately under the biceps, and is concealed by it for a

considerable part of its course (fig. LXXVIII. 4). Arising from the

humerus, on each side of the insertion of the deltoid, it continues its

attachment to the bone all the way down the fore part of the humerus,

to within inch of the joint; it then passes over the joint, adhering

firmly to the anterior ligament (fig. LXXVIII. 4), and is inserted by a

strong tendon into the ulna (fig. LXXVIII. 4). It is a thick and fleshy

muscle, powerfully assisting the action of the biceps.

166. The two extensor muscles are named the triceps and the anconeous

(fig. LXXIX.). The triceps, seated on the back part of the arm, derives

its name from having three distinct points of origin, or three separate

heads (fig. LXXIX. 5); one of which arises from the scapula and two

from the humerus (fig. LXXIX. 5). All these heads adhere firmly to the

humerus, as the brachialis does on the fore part of the arm, down to

within an inch of the joint (fig. LXXIX. 5), where they form a strong

tendon, which is implanted into the olecranon of the ulna (fig. LXXIX.

3); the projection of which affords a lever for increasing the action

of the muscle. In all animals that leap and bound, this process of the

ulna is increased in length in proportion to their power of performing

these movements. The triceps forms an exceedingly thick and strong

muscle, which envelops the whole of the back part of the arm (fig.

LXXIX.); its action is simple and obvious; it powerfully extends the

fore-arm. The anconeous, a small muscle of a triangular form, arising

from the external condyle of the humerus, and inserted into the ulna a

little below the olecranon, assists the action of the triceps.

[Illustration: Fig. LXXIX.

View of the extensor muscles of the fore-arm. 1. The scapula; 2. the

upper part of the humerus; 3. upper end of the ulna; 4. upper end

of the radius; 5. the muscle called _triceps_, the extensor of the

fore-arm.]

167. Such are the motive powers which act upon the fore-arm, and

which produce all the motions of which the hinge-joint of the elbow

renders it capable. But besides flexion and extension, the fore-arm is

capable of the motion of rotation, which is accomplished by means of

the radius. It has been shown (157) that the top of the rounded head of

the radius is excavated into a shallow cup (figs. LXIX. 6, and LXXIII.

4) which receives a corresponding convexity of the humerus (figs.

LXIX. 2, and LXXIII. 2). In consequence of this articulation with the

humerus, the radius, like the ulna, can move backwards and forwards

in flexion and extension, the proper movements of the hinge-joint;

but that portion of the margin of the hinge of the radius which is in

apposition with the ulna is convex (fig. LXIX. 6), and is received into

a semilunar cavity hollowed out in the ulna (fig. LXIX. 5). In this

cavity the rounded head of the radius revolves, the two bones being

held together by the ligament already described (160), which surrounds

the head of the radius (fig. LXXVI. 3), and which holds it firmly

without being adherent to it, and without impeding in any degree the

rotatory motion of the radius. Below, the surface of the radius next

the ulna is hollowed out into a semilunar cavity (fig. LXXXII. 1),

which receives a corresponding convex surface of the ulna (fig. LXXXII.

2), upon which convex surface the radius rolls (fig. LXXXII. 1). Thus,

by the mode in which it is articulated with the ulna above, the radius

turns upon its own axis. By the mode in which it is articulated with

the ulna below, the radius revolves upon the head of the ulna; and, in

consequence of both articulations, is capable of performing the motion

of rotation. Moreover, the hand being attached to the radius through

the medium of the wrist (figs. LXXXII. 1. 4. and LXXXIII. 1. 4) must

necessarily follow every movement of the radius; the rotation of which

brings the hand into two opposite positions. In the one, the palm of

the hand is directed upwards (fig. LXXXII.); in the other, it is turned

downwards (fig. LXXXIII.). When the hand is turned upwards, it is said

to be in the state of _supination_ (fig. LXXXII.); when downwards, in

that of _pronation_ (fig. LXXXIII.). A distinct apparatus of muscles

is provided for effecting the rotation of the radius, in order to

bring the hand into these opposite states: one set for producing its

supination, and another its pronation.

168. The principal supinators arise from the external condyle of the

humerus (fig. LXXX.), and are called long and short (fig. LXXX. 4, 5).

The long supinator extends as far as the lower end of the radius, into

which it is inserted (fig. LXXX. 4): the short supinator surrounds the

upper part of the radius, and is attached to it in this situation (fig.

LXXX. 5.). Moreover, the triceps, being inserted into the radius (164),

often cooperates with the supinators and powerfully assists their

action.

169. The principal pronators are also two, called the round and the

square (figs. LXXXI. and LXXXVI. 1). The round pronator arises from the

internal condyle, and passing downwards, is inserted into the middle

of the radius (fig. LXXXI. 4); the square pronator is a small muscle

between the radius and ulna, at their lower extremities being attached

to each (fig. LXXXVI. 1).

[Illustration: Fig. LXXX.

View of the supinators of the radius and hand. 1. The humerus; 2. the

ulna; 3. the radius; 4. the muscle called the long supinator passing to

be inserted into the lower portion of the radius; 5. the muscle, called

the short supinator, surrounding the upper part of the radius.]

170. The action of these muscles in producing the rotation of the

radius, and so rendering the hand supine or prone, is sufficiently

manifest from the mere inspection of the diagrams (fig. LXXXI. 4).

[Illustration: Fig. LXXXI.

View of the pronators of the hand. 1. Lower end of the humerus; 2. the

radius; 3. the ulna; 4. the muscle called the round _pronator_, one of

the powerful pronators of the hand.]

171. The hand is composed of the carpus, metacarpus, and fingers.

172. The carpus (fig. LXXXII. 4) consists of eight small wedge-shaped

bones, placed in a double row, each row containing an equal number, and

the whole disposed like stones in an arch (fig. LXXXII. 4). They do in

fact form an arch, the convexity of which is upwards, on the dorsal

surface (fig. LXXXIII. 4); and the concavity downwards, on the palmar

surface (fig. LXXXII. 4). But they differ from the stones of an arch

in this, that each bone is joined to its fellow by a distinct moveable

joint, each being covered with a smooth articulating cartilage. At the

same time all of them are tied together by ligaments of prodigious

strength, which cross each other in every direction (fig. LXXVII. 6),

so that the several separate joints are consolidated into one great

joint. The consequence of this mechanism is that some degree of motion

is capable of taking place between the several bones, which, when

multiplied together, gives to the two rows of bones such an extent of

motion, that when the wrist is bent the arch of the carpus forms a kind

of knuckle. By this construction a facility and ease of motion, and

a power of accommodation to motion and force, are obtained, such as

belong to no arch contrived by human ingenuity.

[Illustration: Fig. LXXXII.

1. Lower extremity of the radius; 2. lower extremity of the ulna;

3. styloid process of the ulna; 4. bones of the carpus or wrist;

5. metacarpal bones; 6. first phalanges of the fingers; 7. second

phalanges of the fingers; 8. third phalanges of the fingers.]

173. The metacarpus (fig. LXXXII. 5), the middle portion of the hand,

interposed between the wrist and the fingers, is composed of five

bones, which are placed parallel to each other (fig. LXXXII. 5). They

are convex outwardly, forming the back (fig. LXXXIII. 5), and concave

inwardly, forming the hollow of the hand (fig. LXXXII. 5). They are

large at each end, to form the joints by which they are connected with

the wrist and fingers (figs. LXXXII. and LXXXIII.): they are small in

the middle, in order to afford room for the lodgment and arrangement

of the muscles, that move the fingers from side to side (fig. LXXXVI.

2). Their ends, which are joined to the carpus, are connected by nearly

plane surfaces (figs. LXXXII. and LXXXIII.): their ends, which support

the fingers, are formed into rounded heads, which are received into

corresponding cup-shaped cavities, excavated in the top of the first

bones of the fingers (fig. LXXXII. 5.). The powerful ligaments that

unite these bones pass, both on the dorsal and the palmar surface, from

the inferior extremity of the second row of the carpal to the bases of

the metacarpal bones (fig. LXXVII, 7, 8). The ligaments are arranged in

such a manner as to limit the motions of the joints chiefly to those

of flexion and extension, allowing, however, a slight degree of motion

from side to side.

174. Each of the fingers is composed of three separate pieces of bone,

called phalanges; the thumb has only two (fig. LXXXII. 6, 7, 8): the

phalanges are convex outwardly (fig. LXXXII. 6, 7, 8) for increasing

their strength, and flattened inwardly (fig. LXXXIII. 6, 7, 8) for

the convenience of grasping. The last bones of the fingers, which are

small, terminate at their under ends, in a somewhat rounded and rough

surface (fig. LXXXIII. 8), on which rests the vascular, pulpy, and

nervous substance, constituting the special organ of touch, placed at

the points of the fingers, and guarded on the upper surface by the nail

(fig. LXXXII. 8).

[Illustration: Fig. LXXXIII.

1. Lower extremity of the radius; 2. lower extremity of the ulna; 3.

styloid process of the ulna; 4. bones of the carpus; 5. metacarpal

bones; 6. 7. 8. first, second, and third phalanges of the fingers.]

175. The round inferior extremity of the metacarpus is admitted into

the cavity of the superior extremity of the first phalanx of the five

fingers (figs. LXXXII. and LXXXIII.), and their joints are connected by

lateral and transverse ligaments of great strength (fig. LXXVII. 9).

The situation and direction of the ligaments which unite the several

phalanges of the fingers (fig. LXXVII. 9) are precisely the same as

those of the articulation of the phalanges with the metacarpus (fig.

LXXVII. 7, 8); and the articulation of these bones with one another is

such as to admit only of the motions of flexion and extension.

176. The muscles which perform these motions are seated for the most

part on the fore-arm. Independently of the supinators and pronators

which have been already described (167 et seq.), there are distinct

sets of muscles for bending and extending the wrist and the fingers.

The flexors arise from the internal, and the extensors from the

external, condyle of the humerus (fig. LXIX. 3, 4). The internal

condyle is larger and longer than the external (fig. LXIX. 3, 4); for

the flexors require a larger point of origin and a longer fulcrum

than the extensor muscles; because to the actions of flexion, such as

grasping, bending, pulling, more power is necessary than to the action

of extension, which consists merely in the unfolding or the opening of

the hand previously to the renewal of the grasp.

177. For the same reason, two muscles are provided for flexing,

while only one is provided for extending the fingers. The flexors,

bulky, thick, and strong, are placed on the fore part of the fore-arm

(fig. LXXXIV.). The first, named the superficial flexor (fig. LXXXIV.

1), about the middle of the arm, divides into four fleshy portions,

each of which ends in a slender tendon (fig. LXXXIV. 1). As these

tendons approach the fingers they expand (fig. LXXXIV. 1), and when

in apposition with the first phalanx, split and form distinct sheaths

for the reception of the tendons of the second flexor (fig. LXXXIV.

3). After completing the sheath, the tendons proceed forward along the

second phalanx, into the fore part of which they are implanted, and

the chief office of this powerful muscle is to bend the second joint

of the fingers upon the first, and the first upon the metacarpal bone.

Its action is assisted by a second muscle, called the deep or profound

flexor (fig. LXXXIV. 2), because it lies beneath the former; or the

perforans, because it pierces it. Bulky and fleshy, this second flexor,

like the first, about the middle of the arm, divides into four tendons,

which, entering the sheaths prepared for them in the former muscle

(where the tendons are small and rounded for their easy transmission

and play), pass to the root of the third phalanx of the fingers into

which they are implanted (fig. LXXXIV. 3).

[Illustration: Fig. LXXXIV.

View of the flexor muscles of the fingers. 1. The superficial flexor,

divided and turned aside, to show, 2. the deep flexor; 3. sheaths for

the tendons of the deep flexor, formed by the splitting of the tendons

of the superficial flexor; 4. the anterior annular ligament, divided

and turned aside.]

118. The muscle that extends the fingers, called the common extensor,

is placed on the back part of the fore-arm (fig. LXXXV.), about the

middle of which it divides into four portions which terminate in

so many tendons (fig. LXXXV. 2). When they reach the back of the

metacarpal bones, these tendons become broad and flat, and send

tendinous expansions to each other, forming a strong tendinous sheath

which surrounds the back of the fingers (fig. LXXXV. 2). These

tendinous expansions are inserted into the posterior part of the bones

of the four fingers (fig. LXXXV. 2); and their office is powerfully to

extend all the joints of all the fingers (fig. LXXXV. 2).

179. On both the palmar and dorsal regions of the wrist are placed

ligaments for tying down these tendons, and preventing them from

starting from their situation during the action of the muscles (figs.

LXXXIV. and LXXXV.). On the palmar region an exceedingly strong

ligament passes anteriorly to the concave arch of the carpus (fig.

LXXXIV. 4) for the purpose of tying down the tendons of the flexor

muscles. On the dorsal surface (fig. LXXXV.), a similar ligament,

passing in an oblique direction from the styloid process of the radius

to the styloid process of the ulna (fig. LXXXV. 3), performs the same

office in tying down the tendons of the extensor muscle. Both these

ligaments are called annular.

[Illustration: Fig. LXXXV.

View of the extensor muscles of the fingers. 1. The common extensor,

sending (2 2 2 2) tendons to each finger; 3. the posterior annular

ligament.]

180. In the palm of the hand are placed additional muscles which

assist the flexors of the fingers (fig. LXXXVI. 2), being chiefly

useful in enabling the fingers to perform with strength and precision

short and quick motions. There are especially four small and rounded

muscles (fig. LXXXVI. 2), resembling the earth worm in form and size,

and hence called lumbricales; but as their chief use is to assist the

fingers in executing short and rapid motions, they have also received

the better name of the musculi fidicinales.

[Illustration: Fig. LXXXVI.

1. The muscle called the square pronator; 2. muscles seated in the palm

of the hand, by which, chiefly, the fingers execute short and rapid

motions.]

181. The thumb, in consequence of the comparative looseness of its

ligaments, is capable of a much greater extent of motion than the

fingers, and can be applied to any part of each of the fingers, to

different parts of the hand, and in direct opposition to the power

exerted by the whole of the fingers and hand, in the act of grasping.

The muscles which enable it to perform these varied motions, and which

act powerfully in almost every thing we do with the hand, form a mass

of flesh at the ball of the thumb (fig. LXXXVII. 1), almost entirely

surrounding it. The little finger is also provided with a distinct

apparatus of muscles (fig. LXXXVII. 2), which surrounds its root, just

as those of the thumb surround its ball, in order to keep it firm in

opposition to the power of the thumb in the act of grasping, and in

various other motions.

[Illustration: Fig. LXXXVII.

1. The mass of muscles forming the ball of the thumb; 2. the mass of

muscles forming the ball of the little finger; 3. tendons of one of the

flexor muscles of the fingers; 4. sheaths formed by the tendons of the

superficial flexor for the reception of the tendons of the deep flexor.]

182. The upper extremity is covered by a tendinous expansion or fascia

which envelopes the whole arm, encloses its muscles as in a sheath,

and affords them, in their strong actions, "that kind of support which

workmen feel in binding their arms with thongs." This fascia likewise

descends between many of the muscles, forming strong partitions between

them, and affording points of origin to many of their fibres, scarcely

less fixed than bone itself.

183. From the whole, it appears, that the first joint of the upper

extremities, that of the shoulder, is a ball and socket joint, a joint

admitting of motion in every direction; that the second joint, that of

the elbow, is partly a hinge-joint, admitting of flexion and extension,

and partly a rotation joint, admitting of a turning or rotatory motion;

and that the joints of the wrist and of the fingers are likewise

hinge-joints, admitting at the same time of some degree of lateral

motion. When these various motions are combined, the result is that

the hand can apply itself to bodies in almost every direction, in any

part of the area described by the arm, when all the joints are moved to

their utmost extent. There is thus formed an instrument of considerable

strength, capable of a surprising variety and complexity of movements,

capable of seizing, holding, pulling, pushing and striking with great

power, yet at the same time capable of apprehending the minutest

objects, and of guiding them with the utmost gentleness, precision, and

accuracy, so that there are few conceptions of the designing mind which

cannot be executed by the skilful hand.

184. The lower extremities consist of the thigh, leg, and foot.

185. The osseous part of the thigh consists of a single bone, called

the femur (fig. XXXIV. 4), the longest, thickest, and strongest bone in

the body. It sustains the entire weight of the trunk, and occasionally

much heavier loads superimposed upon it. It is constructed in such

a manner as to combine strength with lightness. This is effected by

rendering the bone what is technically called cylindrical; that is, a

bone in which the osseous fibres are arranged around a hollow cylinder.

There are two varieties of osseous matter,—the compact, in which the

fibres are dense and solid (fig. LXXXVIII. 1), and the spongy, in which

the fibres are comparatively tender and delicate (fig. LXXXVIII. 2).

Both varieties are, indeed, combined, more or less, in every bone,

the compact substance being always external, and the spongy internal;

but in the cylindrical bones the arrangement is peculiar. Every long

or cylindrical bone consists of a body or shaft (fig. LXXXVIII. 4.),

and of two extremities (fig. LXXXVIII. 5). The body is composed

principally of compact substance, which on the external surface is so

dense and solid, that scarcely any distinct arrangement is visible;

but towards the interior this density diminishes; the fibres become

distinct (fig. LXXXVIII. 5), and form an expanded tissue of a cellular

appearance (fig. LXXXVIII. 5), the cells being called cancelli, and

the structure cancellated. In the centre of the bone even the cancelli

disappear; the osseous fibres terminate; and a hollow space is left

filled up, in the natural state, by an infinite number of minute

membranous bags which contain the marrow (fig. LXXXVIII. 3). In the

body of the bone, to which strength is requisite, that part being the

most exposed to external violence, the compact matter is arranged

around a central cavity. By this means strength is secured without

any addition of weight; for the resisting power of a cylindrical body

increases in proportion to its diameter; consequently the same number

of osseous fibres placed around the circumference of a circle produce

a stronger bone than could have been constructed had the fibres been

consolidated in the centre, and had the diameter been proportionally

diminished. The hollow space thus gained in its centre, renders the

bone lighter by the subtraction of the weight of as many fibres as

would have gone to fill up that space; while its strength is not only

not diminished by this arrangement, but positively increased. On the

other hand, at the extremities of the bone, space, not strength, is

required; required for the attachment and arrangement of the tendons

of the muscles that act upon it, and for the formation of joints (fig.

LXXXVIII. 5). Accordingly, at its extremities the bone swells out into

bulky surfaces; but these surfaces are composed, not of dense and solid

substance, but of spongy tissue, covered by an exceedingly thin crust

of compact matter, and so, as by the former expedient strength is

secured without increase of weight, by this, space is obtained without

increase of weight.

[Illustration: Fig. LXXXVIII.

A section of the femur, showing, 1. the compact bony substance; 2. the

spongy or cancellated structure; 3. the internal cavity containing the

marrow; 4. body; 5, extremities of the bone.]

186. The thigh-bone, placed at the under and outer part of the pelvis,

has an oblique direction, the under being considerably nearer its

fellow than the upper end (fig. XXXIV. 4), in order to afford space for

the passages at the bottom of the pelvis, and also to favour the action

of walking. The body of the bone, which is of a rounded form (fig.

XXXIV. 4), is smooth on its anterior surface (fig. XXXIV. 4), where it

is always slightly convex, the convexity being forwards (fig. XXXIV.

4), while its posterior surface is irregular and rough, and forms a

sharp prominent line, termed the linea aspera (fig. XXXV. 4), giving

attachment to numerous muscles.

187. The superior extremity of the femur terminates in a large ball or

head, which forms nearly two-thirds of a sphere (fig. LXXXIX. 4.). It

is smooth, covered with cartilage, and received into the socket of the

ilium called the acetabulum, which, deep as it is, is still further

deepened by the cartilage which borders the brim (fig. LXXXIX. 3). The

brim is particularly high in the upper and outer part, because it is in

this direction that the reaction of the ground against the descending

weight of the trunk tends to dislodge the ball from its socket.

188. Passing obliquely downwards and outwards from the ball, is that

part of the femur which is called the neck (fig. LXXXIX. 5). It spreads

out archlike between the head and the body of the bone, and is more

than an inch in length (fig. LXXXIX. 5). It is thus long in order

that the head of the bone may be set deep in its socket, and that its

motions may be wide, free, and unembarrassed.

[Illustration: Fig. LXXXIX.

1. Lower portion of the ilium; 2. tuberosity of the ischium: 3. socket

for the head of the femur, or thigh-bone; 4. head of the femur; 5. neck

of the femur; 6. the great process of the femur called the trochanter

major; 7. the body of the femur.]

189. From the external surface of the femur, nearly in a line with

its axis, proceeds the largest and strongest bony process of the body

which gives insertion to its most powerful muscles, namely, those that

extend the thigh and that turn it upon its axis (fig. LXXXIX. 6).

Because, from its oblique direction, it rotates the thigh, this process

is called the trochanter, and, from its size, the trochanter major. At

the under and inner part of the neck on the posterior surface of the

bone, is a similar process, but much smaller, called the trochanter

minor (fig. XXXV. 4), into which are inserted the muscles that bend the

thigh.

190. The inferior extremity of the femur, much broader and thicker

than the superior (fig. XC. 1), is terminated by two eminences, with

smooth surfaces, termed condyles (fig. XC. 2), which, articulated with

the tibia, and the patella, form the joint of the knee (figs. XC. 2, 4,

5, and XCI. 1, 2, 3).

[Illustration: Fig. XC.

1. Lower end of the femur; 2. condyles of the femur; 3. upper end of

the tibia; 4. articular surfaces on the head of the tibia on which the

thigh-bone plays; 5. the patella, or knee-pan; 6. upper end of the

fibula, not entering into the knee-joint.]

[Illustration: Fig. XCI.

Posterior view of the bones forming the knee-joint. 1. Lower end of the

femur; 2. upper end of the tibia; 3. articular surfaces on the head of

the tibia, on which the thigh-bone plays; 4. upper end of the fibula,

not entering into the knee joint.]

191. The bones of the leg, two in number, consist of the tibia (fig.

XC. 3) and fibula (fig. XC. 6). The tibia, next to the femur, the

longest bone in the body, is situated at the inner side of the leg

(fig. XC. 3). Its superior extremity is bulky and thick (fig. XC. 3).

The top of it forms two smooth and slightly concave surfaces, adapted

to the convex surfaces of the condyles of the femur (fig. XC. 4, 2).

On its outer side there is a smooth surface, to which the head of the

fibula is attached (fig. XC. 6). Its lower extremity, which is small,

forms a concavity adapted to the convexity of the bone of the tarsus,

called the astragalus, with which it is articulated (fig. XCII. 4.)

Its inner part is produced so as to form the inner ankle (figs. XCII.

2, and XCIII. 3): its outer side is excavated into a semilunar cavity,

for receiving the under end of the fibula, which forms the outer ankle

(figs. XCII. 3, and XCIII. 4).

192. The fibula, in proportion to its length the most slender bone of

the body, is situated at the outer side of the tibia (fig. XC. 6). Its

upper end formed into a head, with a flat surface on its inner side

(figs. XC. 6, and XCI. 4), is firmly united to the tibia (fig. XC. 4).

Its lower end forms the outer ankle, which is lower and farther back

than the inner (fig. XCII. 3, 2).

[Illustration: Fig. XCII.

Anterior view of the bones forming the ankle-joint. 1. Lower end of

the tibia; 2. production of the tibia, forming the inner ankle; 3.

lower end of the fibula, forming the outer ankle; 4. upper part of the

astragalus: these three bones form the ankle-joint; 5 5 5, other bones

of the tarsus; 6 6 6 6 6 metatarsal bones.]

[Illustration: Fig. XCIII.

Posterior view of the bones forming the ankle-joint. 1. Lower end of

the tibia; 2. lower end of the fibula; 3. internal malleolus or ankle;

4. external malleolus or ankle; 5. one of the tarsal bones, called the

astragalus, with which the tibia and fibula are articulated; 6. the os

calcis or heel.]

193. The patella, or knee-pan (fig. XC. 5), is a light but strong

bone, of the figure of the heart as painted on playing-cards, placed

at the fore part of the joint of the knee, and attached by a strong

ligament to the tibia, the motions of which it follows (fig. XC. 5). It

is lodged, when the knee is extended, in a cavity formed for it in the

femur (fig. XC.); when bent, in a cavity formed for it at the fore part

of the knee (fig. XC. 5).

194. The foot consists of the tarsus, metatarsus, and toes.

195. The tarsus, or instep, is composed of seven strong,

irregular-shaped bones, disposed like those of the carpus, in a double

row (fig. XCII. 4, 5). The arrangement of the tarsal bones is such as

to form an arch, the convexity of which above, constitutes the upper

surface of the instep (fig. XCII. 4, 5): in the concavity below are

lodged the muscles, vessels, and nerves that belong to the sole.

196. The metatarsus consists of five bones, which are placed parallel

to each other (fig. XCII. 6), and which extend between the tarsus

and the proper bones of the toes (fig. XCII. 6). Their extremities,

especially next the tarsus, are large, in order that they may form

secure articulations with the tarsal bones (fig. XCII. 6). Their

bodies are arched upwards (fig. XCII. 6), slightly concave below, and

terminate forwards in small, neat, round heads, which receive the

first bones of the toes, and with which they form joints, admitting

of a much greater degree of rotation than is ever actually exercised,

in consequence of the practice of wearing shoes. The natural, free,

wide-spreading form of the toes, and the consequent security with

which they grasp the ground, is greatly impaired by this custom. Taken

together, the bones of the metatarsus form a second arch corresponding

to that of the tarsus (fig. XCVIII. 2).

197. Each toe consists of three distinct bones, called, like those

of the fingers, phalanges (fig. XCVIII.), but the great toe, like

the thumb, has only two (fig. XCVIII.). That extremity of the first

phalanges which is next the metatarsal bones is hollowed into a socket

for the head of the metatarsal bones.

198. Besides the bones already described, there are other small bones,

of the size and figure of flattened peas, found in certain parts of

the extremities, never in the trunk, called sesamoid, from their

resemblance to the seed of the sesamum. They belong rather to the

tendons of the muscles than to the bones of the skeleton. They are

embedded within the substance of tendons, are found especially at the

roots of the thumb and of the great toe, and are always placed in the

direction of flexion. Their office, like that of the patella, which is,

in truth, a bone of this class, is to increase the power of the flexor

muscles by altering the line of their direction, that is, by removing

them farther from the axis of the bone on which they are intended to

act.

199. The ligaments which connect the bones of the lower extremities

are the firmest and strongest in the body. Of these, the fibrous

capsule of the hip-joint (fig. XCIV. 1), which secures the head of the

femur in the cavity of the acetabulum (fig. XCIV.), is the thickest and

strongest. It completely surrounds the joint (fig. XCIV. 1). It arises

from the whole circumference of the acetabulum, and, proceeding in a

direction outwards and backwards, is attached below to the neck of the

femur (fig. XCIV. 1). It is thicker, stronger, and much more closely

attached to the bones than the fibrous capsule of the shoulder-joint

(144), because the hip-joint is formed, not like the shoulder-joint,

for extent of motion, but for strength. Its internal surface is

lined by synovial membrane, and its external surface is covered and

strengthened by the insertion of muscles that move the thigh-bone.

The joint is strengthened by another ligament, which passes from the

inner and fore part of the cavity of the acetabulum (fig. XCV.) to be

inserted into the head of the femur (fig. XCIV.), called the round

ligament, the office of which obviously is to hold the head of the

femur firmly in its socket.

[Illustration: Fig. XCIV.

1. The fibrous capsule of the hip-joint, laid open and turned aside to

show, 2. the round ligament in its natural position.]

[Illustration: Fig. XCV.

A view of the head of the femur drawn out of its socket, and suspended

by the round ligament, to show more clearly the action of the ligament

in retaining the head of the femur in its socket.]

200. Numerous and complicated ligaments connect the bones that form

the knee-joint (fig. XCVI.), and the strength of these powerful bands

is greatly increased by the tendons that move the leg (fig. XCVI. 5),

which pass over, and more or less surround, the joint.

[Illustration: Fig. XCVI.

General view of the ligaments of the knee-joint. 1. Lower end of the

femur; 2. upper end of the tibia; 3. upper end of the fibula; 4. the

patella; 5. united tendons of the extensor muscles; 6. ligaments of

the patella; 7. the capsular investment of the knee; 8. the internal

lateral ligament; 9. the external lateral ligaments; 10. the posterior

ligament; 11. the ligament connecting the tibia and fibula; 12. a

portion of the interosseous ligament.]

201. Strong ligaments maintain in their proper position the bones that

form the ankle-joint (fig. XCVII.), connect the bones of the tarsus

and metatarsus with one another (fig. XCVIII. 1), and articulate the

several phalanges of the toes (fig. XCVIII. 2).

[Illustration: Fig. XCVII.

General view of the posterior ligaments of the ankle-joint. 1. Lower

end of the tibia; 2. lower end of the fibula; 3. astragalus; 4. os

calcis; 5. ligament between the tibia and fibula; 6. ligament passing

from the fibula to the astragalus; 7. ligament passing from the fibula

to the os calcis; 8. ligament passing from the tibia to the astragalus.]

[Illustration: Fig. XCVIII.

General view of the ligaments of the sole of the foot. 1. Ligaments

connecting the bones of the tarsus; 2. ligaments connecting the bones

of the toes.]

202. The joint of the hip, like that of the shoulder, is capable of

flexion, extension, and rotation; but its rotatory motions are to a

much less extent, on account of the greater depth of the acetabulum and

the stronger and shorter fibrous capsule. When the femur is flexed, the

thigh is bent upon the pelvis, and its inferior extremity is carried

forwards. When it is extended, the thigh is carried backwards. The

two thighs may be separated from each other laterally (abduction), or

brought near to each other (adduction), or the one may be made to cross

the other, and they may be rotated outwards or inwards.

203. The apparatus of muscles that produces these varied motions is

seated partly on the trunk and partly on the pelvis. Thus, the powerful

muscle that flexes the thigh, or that carries it forwards, termed

the psoas (fig. XCIX. 1), arises from the last vertebra of the back,

and successively from each vertebra of the loins (fig. XCIX. 1), and

is inserted into the lesser trochanter of the femur (fig. XCIX. 3).

Its action is assisted first by a large and strong muscle named the

iliacus (fig. XCIX. 2), which occupies the whole concavity of the ilium

(fig. XCIX. 2), and which, like the psoas, is inserted into the lesser

trochanter of the femur (fig. XCIX. 3).

[Illustration: Fig. XCIX.

View of the muscles that bend the thigh. 1. The muscle called psoas;

2. the muscle called iliacus; 3. tendons of these muscles, going to be

inserted into the trochanter minor of the femur.]

204. The muscles that extend the thigh, or that carry it backwards,

named the glutæi, the most powerful muscles of the body, are placed

in successive layers, one upon the other, on the back part of the

ilium (fig. C. 1, 2, 3), and are inserted into the linea aspera of the

femur. They constitute the mass of flesh which forms the hip, and their

powerful action in drawing the thigh backwards is assisted by several

other muscles (fig. C. 4, 5, 6). Their action is never perfectly simple

and direct; for those which move the thigh forwards sometimes carry it

inwards, and sometimes outwards; and in like manner, those which move

it backwards, at one time carry it inwards and at another outwards,

according to the direction of the fibres of the muscle and the position

of the limb when those fibres act; while some of them, and more

especially those which carry it backwards, at the same time rotate it,

or roll it upon its axis.

[Illustration: Fig. C.

View of the muscles that extend the thigh. 1. The muscle called glutæus

maximus, removed from its origin, 2, 2, to show the muscles which lie

beneath it; 2. cut edge showing the origin of the same muscle; 3. the

muscle called glutæus medius; 4, 5, 6. smaller muscles, assisting the

action of the glutæi.]

205. The knee is a hinge-joint, admitting only of flexion and

extension, and is therefore provided only with two sets of muscles, one

for bending and the other for extending the leg. The flexors of the leg

arise from the under and back part of the pelvis, are seated on the

back part of the thigh, and are inserted into the upper part either of

the tibia or of the fibula (fig. CI). They consist for the most part of

three muscles, named the semi-tendinosus, the semi-membranosus (fig.

CI. 3), and the biceps of the leg (fig. CI. 1). The tendons of the two

former muscles, in passing to be inserted into the leg, form the inner,

and that of the latter the outer, hamstrings (fig. CI. 4, 5).

[Illustration: Fig. CII.

View of the flexor and extensor muscles of the leg. 1. The biceps of

the leg; 2. tendon of the biceps, inserted into the head of the fibula;

3. the semi-membranosus, passing to be inserted into the head of the

fibula; 4. tendon of the semi-membranosus forming the inner, and 5.

tendon of the biceps forming the outer, hamstring; 6. upper part of the

gastrocnemius muscle; 7. the four large muscles which unite to form the

great extensor muscle of the leg, inserted into 8. the patella; 9. a

portion of the glutæus maximus concealing the other muscles of the hip.]

206. Four large muscles, blended together in such a manner as to form

one muscle of prodigious size, termed the quadriceps cruris (fig. CI.

7), occupying nearly all the forepart and the sides, and a considerable

portion of the back part of the thigh, constitute the great flexor of

the thigh. This enormous mass of muscle arises partly from the ischium,

and partly from the upper part of the femur (fig. CI. 7), and is all

inserted into the patella (fig. CI. 8), which constitutes a pulley for

the purpose of assisting the action of these powerful muscles.

207. The muscles which bend the toes and extend the foot, termed the

gastrocnemii (fig. CII. 1, 2), are placed on the back part of the leg,

and form the mass of muscle which constitutes the calf of the leg (fig.

CII. 1, 2). They arise partly from the lower extremity of the femur

(fig. CII.) and partly from the upper and back part of the fibula and

tibia; and they form the largest and strongest tendon in the body,

termed the tendo achillis (fig. CII. 3), which is implanted into the

heel (fig. CII. 4).

[Illustration: Fig. CII.

View of the muscles which bend the toes, and which, by lifting the

heel, extend the foot. 1. The muscle called gastrocnemius externus,

which, uniting with 2. the gastrocnemius internus, forms 3. the tendo

achillis, which is inserted into 4. the heel.]

[Illustration: Fig. CIII.

View of the muscles which extend the toes and bend the foot. 1. The

common extensor; 2. the tendons of the same muscle inserted into the

toes; 3. the anterior annular ligament of the foot.]

[Illustration: Fig. CIV.

View of the muscles in the sole of the foot. 1 The muscle which draws

the great toe from the other toes; 2. the muscle which draws the little

toe from the other toes; 3. the muscle called the short flexor of the

toes, which assists in bending the four smaller toes.]

208. The muscles which extend the toes and bend the foot are seated

on the fore part of the leg (fig. CIII.); split into tendons like the

analogous muscles of the fingers (fig. CIII. 2); and are bound down

by a ligament (fig. CIII. 3), exactly the same in name, disposition,

and office, as that which belongs to the hand (fig. CIII. 3). Numerous

minute muscles are placed in the sole of the foot (fig. CIV.), which

act on the toes as the small muscles in the palm of the hand act on the

fingers (fig. LXXXVI.).

209. Such are the moving powers which put in action the complicated

mechanism provided for the function of locomotion. And these powers are

adequate to their office; but they are what may be termed expensive

powers; agents requiring a high degree, of organization and the utmost

resources of the economy to support and maintain them. Hence in the

construction of the framework of the machine which they have to move,

whatever mechanical contrivance may economize their labour, is adopted.

The construction, form, and disposition of the several parts of that

framework have all reference to two objects: first, the combination

of strength with lightness; and secondly, security to tender organs,

with the power of executing rapid, energetic, and, sometimes, violent

motions. The combination is effected and the object attained in a mode

complicated in the detail, simple in the design, and perfect in the

result. The weight of the body transmitted from the arch of the pelvis

to a second arch, formed by the neck of the thigh-bone, and from this,

in a perpendicular direction, to a third arch formed by the foot, is

ultimately received by the heel behind, and by the metatarsal bones

and the first phalanges of the toes before, and more especially by the

metatarsal joints belonging to the great and little toe, which have a

special apparatus of muscles, for the purpose of preserving steadily

their relative situation to the heel. The weight of the body is thus

sustained on a series of arches, from which it is, in succession,

transmitted to the ground, where it ultimately rests upon a tripod:

forms known and selected as the best adapted to afford support, and to

give security of position. Columns of compact bone superimposed one

upon another, and united at different points by bands of prodigious

strength, form the pillars of support. But these bony columns never

touch each other; are never in actual contact; are all separated by

layers of elastic matter which, while they assist in binding the

columns together, enable them to move one upon another, as upon so many

pliant springs. The layers of cartilage interposed between the several

vertebræ; the layer of cartilage interposed between the vertebral

column and the pelvis; the layer of cartilage that lines the acetabulum

and that covers the head of the femur; the layer of cartilage that

covers the lower extremity of the femur and the upper extremity of the

tibia and fibula and the tarsus; the successive layers of cartilage

interposed between the several bones of the tarsus; and finally,

the layer of cartilage that covers both the tarsal and the digital

extremities of the metatarsal bones; are so many special provisions to

prevent the weight of the body from being transmitted to the ground

with a shock; and, at the same time, so many barriers established

between the ground and the spinal cord, the brain and the soft and

tender organs contained in the thoracic and abdominal cavities, to

prevent these organs from being injured by the reaction of the ground

upon the body. The excellence of this mechanism is seen in its results;

in contemplating "from what heights we can leap—to what heights we can

spring—to what distances we can bound—how swiftly we can run—how

firmly we can stand—how nimbly we can dance—and yet how perfectly we

can balance ourselves upon the smallest surfaces of support!"

210. It is necessary, in order to complete this general view of the

structure of the human body, and of the combination and arrangement

of its various parts, to denote the several regions into which, for

the purpose of describing with accuracy the situation and relation of

its more important organs, the body is divided. It is not needful to

the present purpose to describe the regions of the head, because its

internal cavity contains only one organ, the brain, and its external

divisions do not differ materially from those which are common

and familiar; but the chest, the abdomen, and the upper and lower

extremities are mapped out into regions, of which it is very important

to have an exact knowledge, which may be acquired by the study of the

annexed diagrams.

[Illustration: Fig. CV.

Anterior view of the regions of the body. 1. Region of the neck; 2.

region of the chest or thorax. Abdominal regions: 3. epigastric; 4.

umbilical; 5. hypogastric region. Regions of the upper extremities. 6.

shoulder; 7. arm; 8. elbow; 9. fore-arm; 10. wrist; 11. ball of thumb;

12. the axilla or armpit. Regions of the lower extremities: 13. thigh;

14. knee; 15. leg; 16. ankle; 17. instep and foot.]

[Illustration: Fig. CVI.

Posterior view of the regions of the body: 18. region to the scapula;

19. of the back; 20. of the loins; 21. of the hips; 22. of the ham; 23.

of the calf of the leg; 24. of the heel and foot.]

[Illustration: Fig. CVII.

Lateral view of the regions of the body: 25. arch of the foot.]

[Illustration: Fig. CVIII.

Anterior view of the situation of the more important internal organs:

1. lungs, right and left; 2. heart; 3. line representing the edge of

the diaphragm; 4. liver; 5. stomach; 6. small intestines; 7. colon; 8.

urinary bladder.]

[Illustration: Fig. CIX.

Posterior view of the situation of the more important internal organs:

9. kidnies, right and left; 10. the course of the spinal cord.]

[Illustration: Fig. CX.

Lateral view of the situation of the more important internal organs.]

The Philosophy of Health; Volume 1 (of 2) or, an exposition of the physical and mental constitution of man · 第 6 / 8 章

101. The ribs successively and considerably increase in length as far