Biomedical Engineering Reference
In-Depth Information
Musculature
Like the posterior thoracic wall, the intrinsic muscles of the
ventrolateral (anterolateral) thoracic wall (
Howell and
Straus, 1933a
) are overlain by muscles of the upper
extremity which embryonically migrate into the area
bringing along the accompanying nerves and vessels. In
nonhuman primates these extrinsic muscles include the m.
subclavius, m. panniculus carnosus, and three pectoral
muscles: mm. pectoralis major, minor, and abdominalis
(
Figure 4.8C,D
). The m. subclavius is similar to that in
humans and passes between the first rib and the inferior
surface of the clavicle. The m. panniculus carnosus arises
from the superficial fascia of the entire lateral torso and
inserts into the humerus with the mm. pectoralis.
Contraction of this muscle usually moves the skin of the
side. There is tremendous variability in the extent and
development of the m. panniculus carnosus in higher
primates, but it is less pronounced in apes than in Old and
New World Monkeys and entirely absent in humans. The
three pectoral muscles in primates also show considerable
variability. In general the m. pectoralis major is the
equivalent of m. pectoralis superficialis in other mammals.
This muscle arises broadly from the sternum and is similar
to that in humans except that it lacks a clavicular head in
most nonhuman primates. The mm. pectoralis minor and
abdominis are equivalent to m. pectoralis profundus in
other mammals. The primary difference between other
mammals and nonhuman primates is that the deep pectoral
layer is divided into two distinct muscles. In both Old and
New World monkeys the m. pectoralis minor generally
inserts onto the humerus or glenohumeral joint capsule
whereas in apes (and humans) it generally inserts into the
coracoid process of the scapula.
The intrinsic muscles of the thorax are innervated
segmentally by ventral rami which parallel segmental
arteries and veins. The intrinsic muscles include the external
and internal intercostal muscles as well as m. transversus
thoracis. The extent of these muscles, the direction of their
fibers, and the positions of the accompanying vessels and
nerves along the caudal (inferior) margin of each rib are
similar to that of other mammals, including humans.
Mediastinum, Autonomic Nerves, and
Thymus
The mediastinum completely separates the right and left
pleural cavities. As in humans and other mammals the
esophagus lies dorsal (posterior) to the trachea and its
bifurcation and to the pericardium and ventral (anterior) to
the thoracic (descending) aorta (
Figure 4.8D
.). The dorso-
ventral narrowing of the thorax results in a shallower
mediastinum in nonhuman primates than in most quadru-
peds, and thus the esophagus lies in closer approximation to
the dorsal (posterior) aspect of the pericardium
(
Figure 4.8D
). The courses of nerves, arteries, veins, and
lymphatic vessels (including the thoracic duct) in the
mediastinum are similar to those of humans (
Kuntz, 1933;
Lineback, 1933b
).
The autonomic nerves of the thorax include both
sympathetic and parasympathetic fibers. The sympathetic
trunks and ganglia lie ventrolateral to the vertebral bodies.
Both white and gray rami communicantes pass between the
trunks and the ventral rami. Preganglionic sympathetic
fibers exit from the spinal cord and travel along white rami
communicantes from spinal nerves T1 through L3 in most
nonhuman primates. Sympathetic fibers destined for
vessels and glands outside the body cavities synapse in the
sympathetic chain ganglia and travel in gray rami com-
municantes to rejoin the ventral rami and distribute to the
body wall. Sympathetic fibers destined for the thoracic
viscera also synapse in the upper thoracic chain ganglia and
leave the sympathetic trunk through thoracic cardiac and
pulmonary nerves, which wrap around the vessels and share
their distribution. Preganglionic sympathetic fibers from
the lowest thoracic and lumbar regions form splanchnic
nerves destined for the preaortic ganglia in the abdominal
region. Preganglionic parasympathetic fibers to viscera in
the thorax and abdomen travel in branches of the vagus
nerves (cranial nerve X) whose central trunks pass dorsal
(posterior) to the roots of the lungs then form the esopha-
geal plexus before accompanying the GI tract into the
abdomen.
The thymus is located in the superior and anterior
mediastina as in humans and reaches its maximum size
early in life, i.e., at approximately 1 year of age in Macacca
mulatta (
Miller and Leonard, 1933
). By adulthood, the
thymus has atrophied considerably with the result that only
scattered remnants of thymic tissue typically remain in the
connective tissue and mark its location in subadults. In
young animals, the thymus can be quite large with
a cervical lobe extending cranially to the 6th tracheal ring
ventral to the trachea and ventral to the great vessels of the
neck. This is continuous with the lateral lobes which flare
out over the pericardium to surround it ventrally and
dorsally as far caudally as the 6th costal cartilage and
cranially curl around the junctions of
Diaphragm
The thoracoabdominal diaphragm is a sheet of skeletal
muscle which completely partitions the thoracic and
abdominal cavities. Its embryonic origin in the cervical
region is evident by its motor innervation by the long
phrenic nerves which traverse the length of the medias-
tinum. The crura of the diaphragm, the position of the
central tendon, the hiatuses for the inferior vena cava,
esophagus, and aorta, and its innervation and blood supply
are similar in all mammals, including humans.
the subclavian
