Thorax 
right fibers of the central tendon at the level of the 
last thoracic vertebra. The aperture of the vena cava 
{foramen venae cavae) is ventrolateral to the esoph- 
ageal hiatus and rests on the right side of the central 
tendon (Figs. 4-10. 4-11). During expiration the 
diaphragmatic dome projects forward to the fourth 
or fifth rib. 
4.4 THORACIC CAVITY 
4.4.1 Pleura and Pleural Sinuses 
Unlike the abdomen, which contains a single sac, 
the chest cavity {cavum thoracis) presents three 
completely separate serous sacs, the two pleurae 
{cavum pleurae smistrum, cavum pleurae dextrum) 
and the pericardium {cavum pencardiacum). The 
pleurae are two serous membranes forming inde- 
pendently closed cavities and into each of which the 
respective lung is invaginated. Appended to, and 
patent with, the right pleural cavity is the inter- 
mediate pleural sac {cavum pleurae intermedium) 
which invests the accessorv and intermediate acces- 
sory lobes of the right lung. The right cavity is thus 
larger than the left. There are two layers of pleura: 
the parietal {pleura parietalis), adherent to the 
thoracic wall and diaphragm and reflected over the 
structures in the middle of the thorax, and the vis- 
ceral layer {pleura pulmonalis) applied over the 
surface of the invaginating lung. The layers, which 
are normally continuous with each other around 
the root of the lung, allow excursion of the lungs 
over the thoracic wall with a minimum of friction. 
Between the two layers is the pleural cavity, nor- 
mally a potential space with a minute amount of 
serous fluid and constituting a true cavity onlv in 
pathology. The very thin visceral pleura is bound to 
the lung surface and dips into the interlobar fissures 
{Jissurae interlobares). Continuous with the pleura 
over the mediastinum, or space between the two 
pleural sacs, at the root of the lung, the visceral 
pleura cannot be detached without laceration of 
lung tissue. The disposition of the pleurae resem- 
bles that of domesticated mammals (Nickel, et al, 
1960). 
The four divisions of the parietal pleura are 
named according to their position in the thorax and 
the structures invested by each are named after their 
division. 
The costal pleura {pleura cos talis) contacts the 
ribs, costal cartilages, intercostal musculature and 
endothoracic fascia. It separates easily from the 
chest wall due to its loose attachment to the endo- 
thoracic fascia. It normally continues ventrally into 
the mediastinal pleura and forms with it a vertical 
sinus, or recess, along the costomediastinal line of 
pleural reflection. 
The diaphragmatic pleura {pleura diaphrag- 
matica) contacts the superior, or convex, surface of 
the diaphragm and invests the caudal margin of the 
two pleural sacs. The phrenic nerves follow the 
pleural extensions over the diaphragm. Adhering 
tightly to diaphragmatic muscle, the pleura covers 
the area not touched by the diaphragmatic pericar- 
dium. It does not extend to the line of attachment of 
the diaphragm to the chest wall, but is separated 
from it by fatty areolar connective tissue. 
The mediastinal pleura {pleura mediastinalis) 
covers the lateral wall of the mediastinum and is 
only in loose contact with the structures against 
which it rests. It consists of a double fold that sepa- 
rates to pass around each side of the pericardial 
space, joining again dorsally to enclose the peri- 
cardium. In the cranial part of the mediastinum it 
extends without interruption from the sternum to 
spine; in the caudal part it reflects from the peri- 
cardium over the root of the lung and becomes con- 
tinuous with the costal pleura. 
The cervical pleura {pleura cervicalis), or cupula 
pleurae, is bounded medially by the trachea and 
attaches dorsally to the ventral border of the trans- 
verse process of the seventh cervical vertebra. It is 
covered by the scalene muscles and its surface topog- 
raphv is indicated by a craniallv convex curve 
drawn from the center of the sternoclavicular joint 
to the junction of the sternal and middle thirds of 
the clavicle. The apices of the lung fill the domes 
completely during normal inspiration. The dorsal 
and middle scalene fibers lie on the lateral surface 
of the pleura before attaching to the upper surface 
of the first rib. The subclavian artery {arteria sub- 
clavia) lies in a groove on the medial and dorsal 
aspect of the pleural dome. The internal thoracic 
vessels, the beginning of vertebral and intercostal 
arterialization, the inferior ganglion of the cervical 
chain and the lower trunk of the brachial plexus 
also rest on the cervical pleura. 
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