THE MUSCLES OF THE THORAX. 393 
The longus colli is a flattened muscular band extending from the third thoracic 
vertebra to the atlas. It is divisible into three portions —a vertical, a lower 
oblique, and an upper oblique portion. 
The vertical portion of the muscle arises from the bodies of the first three 
thoracic and the last three cervical vertebre ; and passing vertically upwards, 
is inserted into the bodies of the second, third, and fourth cervical vertebre. 
The lower oblique portion arises from the bodies of the first three thoracic 
vertebre, and is inserted into the anterior tubercles of the fifth and sixth cervical 
vertebree. ; 
The upper oblique portion arises from the anterior tubercles of the transverse 
processes of the third, fourth, and fifth cervical vertebree, and is directed upwards, to 
be inserted into the anterior tubercle of the atlas. 
The longus colli clothes the front of the vertebral column in the neck, and 
is separated by the deep cervical fascia from the carotid vessels, pharynx, and 
cesophagus. 
The rectus capitis lateralis, in series with the posterior inter - transverse 
muscles in the neck, arises from the transverse process of the atlas, and is inserted 
into the under surface of the ex-occipital bone. It is placed alongside the recti 
capitis antici, separated from them by the anterior primary division of the first 
cervical nerve. 
NERVE SUPPLY. 
The prevertebral muscles are all supplied by anterior primary divisions of the cervical spinal 
nerves: the rectus capitis anticus minor, and rectus capitis lateralis, by the loop between the first 
two nerves; the rectus capitis anticus major by the first four; the longus colli by the second, 
third, and fourth ; the scaleni by the lower four or five cervical nerves. 
ACTIONS. 
The movements produced by these muscles are considered along with those of other muscles 
acting on the head, spinal column, and thorax. 
TER MIE SCLES O8) WER THORAX 
MUSCLES OF RESPIRATION. 
The muscles which complete the boundaries of the thorax are the diaphragm 
and intercostal muscles (external and internal), along with three series of 
smaller muscles—the triangularis sterni, the levatores costarum, and the infra- 
costales. 
The intercostal muscles are arranged in eleven pairs, forming thin layers 
filling up the intercostal spaces. 
The external muscle arises from the sharp lower border of the rib, and 
is directed downward and forward, to be inserted into the outer edge of the 
upper border of the rib below. It extends from the tubercle of the rib 
behind nearly to the costal cartilage in front. The anterior “intercostal 
aponeurosis is continuous with it anteriorly, and extends forwards to the side of 
the sternum. 
The internal muscle arises from the costal cartilage and the inner edge of the 
subcostal groove, and is directed downwards and backwards, to be inserted into the 
inner edge of the upper border of the rib and costal cartilage below. It extends 
from the side of the sternum in front to the angle of the rib behind, where it 
becomes continuous with the posterior intercostal aponeurosis extending to the 
tubercle of the rib. 
The external intercostal muscles are covered by the pectoral muscles, serratus 
magnus and the muscles of the back; the internal muscles are in contact with 
the pleura. The intercostal vessels and nerve lie between the two muscles 
posteriorly. 
The levatores costarum are in series with the external intercostal 
muscles. They are twelve small slips arising from the transverse processes of 
the seventh cervical and upper eleven thoracic vertebre. They spread out in 
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