of the muscles of opposite sides decussate in the median plane, in the inferior part of the pharyngeal wall.

Nerve-Supply. The muscle is innervated through the pharyngeal plexus, by the accessory

nerve.

The Muscles of the Soft Palate.

The soft palate and uvula form a muscular fold, covered on each surface by mucous membrane, projecting backwards into the pharynx, and forming the posterior

parts of the floor of the nasal cavities and the roof of the mouth. The muscular fold is composed of five pairs of muscles-the pharyngopalatinus, m. uvulæ, levator veli palatini, tensor veli palatini, and glossopalatinus.

The pharyngopalatinus muscle has been already described (p. 465).

FIG. 413.-LATERAL VIEW OF THE WALL OF THE PHARYNX.

The m. uvulæ

(O.T. azygos uvulæ) consists of two narrow bundles enclosed, along with the insertion of the levator veli palatini, between the layers of the pharyngopalatinus. The slips arise from the posterior nasal spine and the aponeurosis of the soft palate, and unite as they proceed backwards to end in the uvula. M. Levator Veli Palatini.The levator veli palatini has a double origin: (1) from the inferior surface of the apex of the petrous portion of the tem

poral bone, and (2) from the inferior part of the cartilaginous part of the auditory tube. It passes obliquely downwards and medially, across the superior border of the superior constrictor muscle, and enters the soft palate between the two layers of the pharyngopalatinus muscle.

It is inserted into the aponeurosis of the soft palate, and some of its fibres become continuous with those of the opposite muscle.

It is separated from the tensor veli palatini muscle by the auditory tube and the deeper layer of the pharyngopalatinus muscle.

M. Tensor Veli Palatini.-The tensor veli palatini arises (1) from the scaphoid fossa and the angular spine of the sphenoid bone, and (2) from the lateral side of the cartilaginous part of the auditory tube.

It descends, between the internal pterygoid muscle and the medial pterygoid lamina, and ends in a tendon which hooks round the pterygoid hamulus. The tendon is inserted, beneath the levator veli palatini, into the posterior border of the hard palate, and into the aponeurosis of the soft palate.

M. Glossopalatinus. The glossopalatinus (O.T. palatoglossus), occupying the inferior surface of the soft palate and the glosso-palatine arch, has already been described with the muscles of the tongue (p. 463).

Nerve-Supply. The muscles of the soft palate (except the tensor veli palatini, which is innervated through the otic ganglion by the trigeminal nerve) are supplied through the pharyngeal plexus by the accessory nerve.

Actions of the Muscles of the Pharynx and Soft Palate. The muscles of the pharynx and soft palate are chiefly brought into action in the act of swallowing. This act is divided into a voluntary stage, in which the bolus lies anterior to the arches of the fauces, and an involuntary stage, during which the food passes from the mouth through the pharynx. The movements occurring during the passage of food through the mouth are as follows: the cheeks are compressed by the action of the buccinator muscles; the tongue, hyoid bone, and thyreoid cartilage are successively raised upwards by the action of the muscles which close the mouth and elevate the hyoid bone. By these means the food is pushed backwards between the palatine arches.

At the same time, by the contraction of the glosso-palatinus and pharyngo-palatinus, the palatine arches of the fauces are narrowed, while the muscles of the soft palate, contracting, tighten the soft palate, and by bringing it in contact with the posterior wall of the pharynx, shut off the nasal portion of the cavity. The elevation of the tongue, hyoid bone, and larynx simultaneously causes the elevation of the epiglottis and the superior aperture of the larynx, which is closed by the approximation of the arytenoid cartilages and the combined action of laryngeal muscles (arytenoideus, thyreoarytenoideus, and thyreoepiglotticus). The food thus slips over the anterior surface of the epiglottis and the closed superior aperture of the larynx, and between the palatine arches on either side, into the pharynx. It is now clasped by the constrictor muscles, which, by their contractions, force it down into the oesophagus. The contraction of the constrictor muscles results in a flattening of the pharynx and elevation of its anterior attachments.

During the act of swallowing, it is generally thought that the auditory tube is opened by the contraction of the tensor veli palatini muscle, which arises from it. It has been held, on the other hand, that the auditory tube is closed during swallowing by the compression of its wall by the contraction of the levator veli palatini.

Deep Lateral and Prævertebral Muscles of the Neck.

Three series of muscles are comprised in this group: (1) vertebro-costal (scaleni, anterior, medius, and posterior), (2) vertebro-cranial (longus capitis and rectus capitis anterior, and lateralis), and (3) vertebral (longus colli). They clothe the anterior surface of the cervical portion of the vertebral column for the most part, and are in relation anteriorly with the pharynx and cesophagus, and the large vessels and nerves of the neck.

M. Scalenus Anterior.-The scalenus anterior (O.T. anticus) arises from the anterior tubercles of the transverse processes of the third, fourth, fifth, and sixth cervical vertebræ.

It descends, posterior to the carotid sheath and subclavian vein, to be inserted into the scalene tubercle and ridge on the first rib (Fig. 414, p. 468).

It is separated posteriorly from the scalenus medius by the roots of the brachial plexus, the subclavian artery, and the pleura, and it is concealed by the sternomastoid muscle.

M. Scalenus Medius.-The scalenus medius arises from the posterior tubercles of the transverse processes of the cervical vertebræ, from the second to the sixth inclusive.

It descends in the posterior triangle, behind the subclavian artery and the roots of the brachial plexus, to be inserted into the rough impression on the first rib behind the subclavian groove (Fig. 414, p. 468). The muscle is pierced by the dorsal scapular and long thoracic nerves.

It is separated from the scalenus anterior by the subclavian artery and the roots of the brachial plexus.

M. Scalenus Posterior. The scalenus posterior arises, behind the scalenus medius, from the posterior tubercles of the fourth, fifth, and sixth cervical transverse processes. It is inserted into an impression on the outer side of the second rib.

is divisible into three portions-a vertical, an inferior oblique, and a superior oblique portion.

The vertical portion of the muscle arises from the bodies of the first three thoracic and the last three cervical vertebræ.

Passing vertically upwards, it is inserted into the bodies of the second, third, and fourth cervical vertebræ.

The inferior oblique portion arises from the bodies of the first three thoracic vertebræ.

It is inserted into the anterior tubercles of the fifth and sixth cervical vertebræ. 31 a

The superior oblique portion arises from the anterior tubercles of the transverse processes of the third, fourth, and fifth cervical vertebræ.

It is directed upwards, to be inserted into the anterior tubercle of the atlas.

Nerve-Supply. It is supplied by nerves from the anterior rami of the second, third, and fourth cervical nerves.

Action. A flexor of the vertebral column.

M. Rectus Capitis Lateralis.-The rectus capitis lateralis, in series with the posterior inter-transverse muscles in the neck, arises from the transverse process of the atlas.

It is inserted into the inferior surface of the jugular process of the occipital bone. It is placed alongside the rectus capitis anterior, separated from it by the anterior ramus of the first cervical nerve.

Nerve-Supply.-The loop between the anterior rami of the first two cervical nerves.

Actions. A lateral flexor of the head and vertebral column. The movements produced by these muscles are considered along with those of other muscles acting on the head, vertebral column, and thorax (pp. 445, 446).

THE MUSCLES OF THE 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 transversus thoracis, the levatores costarum, and the subcostal muscles.

Mm. Intercostales. The intercostal muscles are arranged in eleven pairs, which occupy the intercostal spaces.

Each external muscle arises from the sharp lower border of a rib, and is directed inferiorly and anteriorly, to be inserted into the external edge of the superior border of the rib below. It extends from the tubercle of the rib posteriorly nearly to the costal cartilage anteriorly. The anterior intercostal aponeurosis is continuous with it anteriorly, and extends forwards to the side of the sternum.

Each internal muscle arises from the costal cartilage and the internal or superior edge of the costal groove, and is directed inferiorly and posteriorly, to be inserted into the internal edge of the superior border of the rib and costal cartilage below. It extends from the side of the sternum anteriorly to the angle of the rib posteriorly, where it is replaced by the posterior intercostal aponeurosis extending to the tubercle of the rib.

The superficial surface of the external muscle is covered by the muscles of the chest, axilla, abdomen, and back. The deep surface of the internal muscle is in contact with the pleura.

Mm. Levatores Costarum. 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 vertebræ. Each spreads out in a fan-like manner as it descends to the lateral surface of the rib immediately below where it is inserted posterior to the angle.

Mm. Subcostales.-The subcostal muscles are slips of muscles found on the internal surface of the lower ribs near their angles. They are in series with the internal intercostal muscles, but pass over the deep surface of several ribs.

M. Transversus Thoracis. The transversus thoracis (O.T. triangularis sterni) occupies the posterior aspect of the anterior thoracic wall, and is separated from the costal cartilages by the internal mammary vessels. It arises from the posterior surface of the xiphoid process and body of the sternum as high as the level of the third costal cartilage.

From that origin its fibres radiate laterally, the lower horizontally, the upper fibres obliquely upwards, to be inserted into the second, third, fourth, fifth, and sixth costal cartilages. The muscle is continuous below with the transversus abdominis.