> manifest a greater relative proportion to the ventral cavity and organs.

At the adult age, when sexual peculiarities have become fully marked,

the thoracic organs of the male body predominate over those of the

abdomen, whilst in the female form the ventral organs take precedence as

to development and proportions. This diversity in the relative capacity

of the thorax and abdomen at different stages of development, and also

in persons of different sexes, stamps each individual with

characteristic traits of physical conformation; and it is required that

we should take into our consideration this normal diversity of

character, while conducting our examinations of individuals in reference

to the existence of disease.



The heart varies in some measure, not only as to size and weight, but

also as to position, even in healthy individuals of the same age and

sex. The level at which the heart is in general found to be situated in

the thorax is that represented in PLATE 23, where the apex points to the

sixth intercostal space on the left side above K, while the arch of the

aorta rises to a level with C, the second costal cartilage. In some

instances, the heart may be found to occupy a much lower position in the

thorax than the one above mentioned, or even a much higher level. The

impulse of the right ventricle, F, has been noticed occasionally as

corresponding to a point somewhat above the middle of the sternum and

the intercostal space between the fourth and fifth left costal

cartilages; while in other instances its beating was observable as low

down as an inch or more below the xiphoid cartilage, and these

variations have existed in a state of health.



Percussion over the region of the heart yields a dull flat sound. The

sound is dullest opposite the right ventricle, F; whilst above and to

either side of this point, where the heart is overlapped by the anterior

shelving edges of both lungs, the sound is modified in consequence of

the lung's resonant qualities. The heart-sounds, as heard through the

stethoscope, in valvular disease, will, of course, be more distinctly

ascertained at the locality of F, the right ventricle, which is

immediately substernal. While the body lies supine, the heart recedes

from the forepart of the chest; and the lungs during inspiration

expanding around the heart will render its sounds less distinct. In the

erect posture, the heart inclines forwards and approaches the anterior

wall of the thorax. When the heart is hypertrophied, the lungs do not

overlap it to the same extent as when it is of its ordinary size. In the

latter state, the elastic cushion of the lung muffles the heart's

impulse. In the former state, the lung is pushed aside by the overgrown

heart, the strong muscular walls of which strike forcibly against the

ribs and sternum.



The thorax is separated from the abdomen by the moveable diaphragm. The

heart, F E, lies upon the diaphragm, L L*. The liver, M, lies

immediately beneath the right side of this muscular septum, L*, while

the bulging cardiac end of the stomach, O, is in close contact with it

on the left side, L. As these three organs are attached to the

diaphragm--the heart by its pericardium, the stomach by the tube of the

oesophagus, and the liver by its suspensory ligaments--it must happen

that the diaphragm while descending and ascending in the motions of

inspiration and expiration will communicate the same alternate motions

to the organs which are connected with it.



In ordinary respiration the capacity of the thorax is chiefly affected

by the motions of the diaphragm; and the relative position which this

septum holds with regard to the thoracic and abdominal chambers will

cause its motions of ascent and descent to influence the capacity of

both chambers at the same time. When the lungs expand, they follow the

descent of the diaphragm, which forces the abdominal contents downwards,

and thus what the thorax gains in space the abdomen loses. When the

lungs contract, the diaphragm ascends, and by this act the abdomen gains

that space which the thorax loses. But the organs of the thoracic cavity

perform a different office in the economy from those of the abdomen. The

air which fills the lungs is soon again expired, whilst the ingesta of

the abdominal viscera are for a longer period retained; and as the

space, which by every inspiration the thorax gains from the abdomen,

would cause inconvenient pressure on the distended organs of this latter

cavity, so we find that to obviate this inconvenience, nature has

constructed the anterior parietes of the abdomen of yielding material.

The muscular parietes of the abdomen relax during every inspiration, and

thus this cavity gains that space which it loses by the encroachment of

the dilating lungs.



The mechanical principle upon which the abdominal chamber is

constructed, enables it to adjust its capacity to such exigence or

pressing necessity as its own visceral organs impose on it, from time to

time; and the relation which the abdominal cavity bears to the thoracic

chamber, enables it also to be compensatory to this latter. When the

inspiratory thorax gains space from the abdomen, or when space is

demanded for the increasing bulk of the alimentary canal, or for the

enlarging pregnant uterus; or when, in consequence of disease, such as

dropsical accumulation, more room is wanted, then the abdominal chamber

supplies the demand by the anterior bulge or swell of its expansile

muscular parietes.



The position of the heart itself is affected by the expansion of the

lungs on either side of it. As the expanding lungs force the diaphragm

downwards, the heart follows it, and all the abdominal viscera yield

place to the descending thoracic contents. In strong muscular efforts

the diaphragm plays an important part, for, previously to making forced

efforts, the lungs are distended with air, so as to swell and render

fixed the thoracic walls into which so many powerful muscles of the

shoulders, the neck, back, and abdomen, are inserted; at the same time

the muscular diaphragm L L*, becomes tense and unbent from its arched

form, thereby contracting abdominal space, which now has no compensation

for this loss of space, since the abdominal parietes are also rendered

firm and unyielding. It is at this crisis of muscular effort that the

abdominal viscera become impacted together; and, acting by their own

elasticity against the muscular force, make an exit for themselves

through the weakest parts of the abdominal walls, and thus herniae of

various kinds are produced. The most common situations of abdominal

herniae are at the inguinal regions, towards which the intestines, T T,

naturally gravitate; and at these situations the abdominal parietes are

weak and membranous.



The contents of a hernial protrusion through the abdominal parietes,

correspond in general with those divisions of the intestinal tube, which

naturally lie adjacent to the part where the rupture has taken place. In

the umbilical hernia it is either the transverse colon S*, or some part

of the small intestine occupying the median line, or both together, with

some folds of the omentum, which will be found to form the contents of

this swelling. When the diaphragm itself sustains a rupture in its left

half, the upper portion of the descending colon, S, protrudes through

the opening. A diaphragmatic hernia has not, so far as I am aware, been

seen to occur in the right side; and this exemption from rupture of the

right half of the diaphragm may be accounted for anatomically, by the

fact that the liver, M, defends the diaphragm at this situation. The

liver occupies the whole depth of the right hypochondrium; and

intervenes between the diaphragm L*, and the right extremity of the

transverse colon, S**.



The contents of a right inguinal hernia consist of the small intestine,

T. The contents of the right crural hernia are formed by either the

small intestine, T, or the intestinum caecum, S***. I have seen a few

cases in which the caecum formed the right crural hernia. Examples are

recorded in which the intestine caecum formed the contents of a right

inguinal hernia. The left inguinal and crural herniae contain most

generally the small intestine, T, of the left side.



The right lung, I*, is shorter than the left; for the liver, M, raises

the diaphragm, L, to a higher level within the thorax, on the right

side, than it does on the left. When the liver happens to be diseased

and enlarged, it encroaches still more on thoracic space; but,

doubtless, judging from the anatomical connexions of the liver, we may

conclude that when it becomes increased in volume it will accommodate

itself as much at the expense of abdominal space. The liver, in its

healthy state and normal proportions, protrudes for an inch (more or

less) below the margins of the right asternal ribs. The upper or convex

surface of the liver rises beneath the diaphragm to a level

corresponding with the seventh or sixth rib, but this position will vary

according to the descent and ascent of the diaphragm in the respiratory

movements. The ligaments by which the liver is suspended do not prevent

its full obedience to these motions.



The left lung, I, descends to a lower level than the right; and the left

diaphragm upon which it rests is itself supported by the cardiac end of

the stomach. When the stomach is distended, it does not even then

materially obstruct the expansion of the left lung, or the descent of

the left diaphragm, for the abdominal walls relax and allow of the

increasing volume of the stomach to accommodate itself. The spleen, R,

is occasionally subject to an extraordinary increase of bulk; and this

organ, like the enlarged liver and the distended stomach, will, to some

extent, obstruct the movements of the diaphragm in the act of

respiration, but owing to its free attachments it admits of a change of

place. The abdominal viscera, one and all, admit of a change of place;

the peculiar forms of those mesenteric bonds by which they are

suspended, allow them to glide freely over each other; and this

circumstance, together with the yielding nature of the abdominal

parietes, allows the thoracic organs to have full and easy play in the

respiratory movements performed by agency of the diaphragm.



The muscles of respiration perform with ease so long as the air has

access to the lungs through the normal passage, viz., the trachea. While

the principle of the thoracic pneumatic apparatus remains underanged,

the motor powers perform their functions capably. The physical or

pneumatic power acts in obedience to the vital or muscular power, while

both stand in equilibrium; but the ascendancy of the one over the other

deranges the whole thoracic machine. When the glottis closes by muscular

spasm and excludes the external air, the respiratory muscles cease to

exert a motor power upon the pulmonary cavity; their united efforts

cannot cause a vacuum in thoracic space in opposition to the pressure of

the external air. When, in addition to the natural opening of the

glottis, a false opening is made in the side at the point K, the air

within the lung at I, and external to it in the now open pleural cavity,

will stand in equilibrio; the lung will collapse as having no muscular

power by which to dilate itself, and the thoracic dilator muscles will

cease to affect the capacity of the lung, so long as by their action in

expanding the thoracic walls, the air gains access through the side to

the pleural sac external to the lung.



Whether the air be admitted into the pleural sac, by an opening made in

the side from without, or by an opening in the lung itself, the

mechanical principle of the respiratory apparatus will be equally

deranged. Pneumo-thorax will be the result of either lesion; and by the

accumulation of air in the pleura the lung will suffer pressure. This

pressure will be permanent so long as the air has no egress from the

cavity of the pleura.



The permanent distention of the thoracic cavity, caused by the

accumulation of air in the pleural sac, or by the diffusion of air

through the interlobular cellular tissue consequent on a wound of the

lung itself, will equally obstruct the breathing; and though the

situation of the accumulated air is in fact anatomically different in

both cases, yet the effect produced is similar. Interlobular pressure

and interpleural pressure result in the same thing, viz., the permanent

retention of the air external to the pulmonary cells, which, in the

former case, are collapsed individually; and, in the latter case, in the

mass. Though the emphysematous lung is distended to a size equal to the

healthy lung in deep inspiration, yet we know that emphysematous

distention, being produced by extrabronchial air accumulation, is, in

fact, obstructive to the respiratory act. The emphysematous lung will,

in the same manner as the distended pleural sac, depress the diaphragm

and render the thoracic muscles inoperative. The foregoing observations

have been made in reference to the effect of wounds of the thorax, the

proper treatment of which will be obviously suggested by our knowledge

of the state of the contained organs which have suffered lesion.







DESCRIPTION OF PLATE 23.



A. Upper end of the sternum.



B B.* First pair of ribs.



C C.* Second pair of ribs.



D. Aorta, with left vagus and phrenic nerves crossing its transverse

arch.



E. Root of pulmonary artery.



F. Right ventricle.



G. Right auricle.



H. Vena cava superior, with right phrenic nerve on its outer border.



I I*. Right and left lungs collapsed, and turned outwards, to show the

heart's outline.



K K*. Seventh pair of ribs.



L L*. The diaphragm in section.



M. The liver in section.



N. The gall bladder with its duct joining the hepatic duct to form the

common bile duct. The hepatic artery is seen superficial to the common

duct; the vena portae is seen beneath it. The patent orifices of the

hepatic veins are seen on the cut surface of the liver.



O. The stomach.



P. The coeliac axis dividing into the coronary, splenic and hepatic

arteries.



Q. Inferior vena cava.



R. The spleen.



S S* S**. The transverse colon, between which and the lower border of

the stomach is seen the gastro-epiploic artery, formed by

the splenic and hepatic arteries.



S***. Ascending colon in the right iliac region.



T. Convolutions of the small intestines distended with air.