On the medial part of the clavicle
is a broad rough surface, the costal tuberosity (rhomboid impression), rather more than 2 cm. in length, for the attachment of the costoclavicular ligament
. The rest of this surface is occupied by a groove
, which gives attachment to the Subclavius
; the coracoclavicular fascia
, which splits to enclose the muscle, is attached to the margins of the groove. Not infrequently this groove is subdivided longitudinally by a line which gives attachment to the intermuscular septum
of the Subclavius.