_c′_, Cleido-occipitalis muscle; _d_, sterno-cephalicus; _f_, _f′_,
long and external heads of triceps; _g_, superficial pectoral
muscle; _h_, _h′_, posterior and anterior deep pectoral muscles;
_i_, _i′_, serratus magnus; _k_, latissimus dorsi; _l_, obliquus
abdominis externus; _v′_, biceps brachii; _w_, splenius; _x_,
rhomboideus; _y_, trachelo-mastoideus; _z_, supraspinatus; _z′_,
infraspinatus; _z″_, tendon of insertion of _z′_; _1′_, cartilage of
scapula; _2_, tuberosity of spine of scapula; _3_, acromion; _5_,
external tuberosity of humerus; _6_, deltoid tuberosity; _8_,
olecranon; _26_, transverse processes of cervical vertebræ; _27_,
posterior auricular muscles; _X_, wing of atlas. (After
Ellenberger-Baum, Anat. für Künstler.)
]
The =obliquus abdominis internus= is more developed and has an
additional origin from the lumbo-dorsal fascia. The aponeurosis blends
with that of the external oblique near the linea alba, and detaches a
layer which assists in the formation of the internal sheath of the
rectus.
The =rectus abdominis= arises on the lateral border of the sternum as
far forward as the third costal cartilage. The two muscles are
separated, except near the pelvis, by an interval varying from two to
four inches (ca. 5 to 10 cm.), so that this part of the abdominal wall
is entirely fibrous. (The umbilicus is in a transverse plane through the
third lumbar vertebra.) There are five tendinous inscriptions, on the
third of which is a foramen for the passage of the subcutaneous
abdominal vein (milk vein). The prepubic tendon has, in addition to
branches inserted into the ilio-pectineal eminences, a strong attachment
to the median common tendon of the adductors of the thigh, so that the
abdominal wall is strongly retracted and almost vertical at its junction
with the pelvis.
The =transversus abdominis= presents no striking differential features.
The transversalis fascia is strong and distinct except over the
diaphragm.