The course of the cephalic vein (p. 216) should be traced before
separating the muscles of the front of the forearm.
Note the supraspinous and infraspinous fasciae cover-
ing the corresponding portions of the lateral surface of the
shoulder.
(a) The cleidohumeralis. Origin: Lateral portion of the
clavicle and the cleidohumeral ligament. Insertion: Anterior
surface of the humerus in its distal third. The muscle is a
continuation of the basioclavicularis, but represents the
brachial part of the brachiocephalic muscle, which, in
many mammals with reduced clavicle, extends from the
mastoid portion of the skull to the front of the arm. The
cervical part is the cleidomastoideus.
THE ANTERIOR LIMB.
(b) The deltoideus:


Acromial portion.
Scapular portion.
portion of deltoid tuberosity.
Origin: Infraspinous fascia.
211


Origin: The Acromion. Insertion: Distal


The end of


the muscle forms a curved line over the dorsal portion of the


infraspinatus, leaving only a
small triangular portion of
the latter exposed. Insertion:
The distal portion of the mus-
cle passes beneath the meta-
cromion, which also serves as
a point of attachment, and is
replaced on the lateral surface
of the humerus, beneath the
acromial portion, by a long
thin tendon, through which
it is inserted.
~The scapular portion of the|


deltoideus should be separated
from the infraspinatus and divid-
‘ed, the distal end being reflected
together with the metacromion.
(d) The infraspinatus.
Origin: Posterior por-
tion of the lateral sur-
face of the scapula, in-
cluding the spine. In-
sertion: Greater tub-
ercle of the humerus.
The muscle fills the
infraspinous fossa.
