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NEW VIEW OF THE MECHANISM OF RESPIRATION 287
PLATE LXXVIII
dragging down the ribs and sternum, and so reducing the size of the thoracic cavity, d, Pectoralis major with its muscular
fibres drawn up ; e, latissinius dorsi with its muscular fibres drawn up ; /, serratus magnus ; g, oljliquis externus ; h, crest of
the ilium.
When the arms are raised and fixed, the pectoral muscles and latissinius dorsi draw up the ribs as in forced inspiration. In this
movement ihe abdominal muscles (external oblique, internal oblique, transversalis and rectal abdominal muscles) take part.
Fig. 3. a, External intercostal muscles ; b, internal intercostal muscles ; c, serratus posticus muscles inferior ; d, lumbar fascia ;
e, internal oblique muscle ; f,ff", rectus abdominis muscle covered with its sheath ; g, crest of the iliac bone.
The external and internal intercostal muscles cross each other obliquely, and when they contract take a prominent part M'ith tlie
pectoralis minor muscles and serratus magnus muscles in elevating the ribs during inspiration. The ribs are forcibly dragged downwards
during expiration by the contraction of the two recti abdominal muscles aided by the external and internal oblique muscles.
The numerals from 8 to 12 inclusive indicate the positions of the five lower ribs.
Fig. 4. a, Lower portion of sternum ; b, symphysis pubis; c, the right rectus abdominis muscle, showing the vertical direction
of its muscular fibres ; d, e, the right and left recti abdominis muscles, the latter cut across ; /, transversalis abdominis. This muscle
by its contractions plays an important part in the expulsive efforts of the abdomen in urination, defaecation, and parturition.
g, External intercostal muscles ; h, h', internal intercostal muscles ; i, lumbar fascia ; j, crest of the ilium.
The numerals from 5 to 12 inclusive indicate the positions of the ribs. The recti and transverse abdominal muscles run at right
angles to each other, and by their united contractions, aided by the external and internal oblique muscles, diminish the cavity of the
abdomen during expiration in all its diameters. The chest muscles (muscles of inspiration) contract or shorten when the abdominal
muscles (muscles of expiration) relax and elongate, and vice vend—the cavity of the thorax being increased when that of the abdomen
is diminished, and conversely. The complemental movements referred to are best seen in forced inspiration and expiration.
Fig. 50.
Fir,. 51.
Fig. 50.—Anterior view of the deep muscles of the thorax and abdomen in man (the recti abdominis, which are superficial,
excepted), a. Spine : b, symphysis pubis ; c, c', ribs ; d, costal cartilages ; e, sternum ; /, externa intercostal muscles ; g, internal inter-
costal muscles ; attachment of the rectus abdominis to the cartilages of the ribs; %,%, recti abdominis; j,
abdominis ; Ic, transversalis abdominis.
tbe internal oblique