The portion of the muscle which is inserted on the cervical transverse processes (_f″_) is sometimes distinguished as the =longissimus cervicis=; it is not well separated from the rest of the muscle in the cat. The =longissimus capitis= (Fig. 69, _c_; Fig. 73, _g_) is to be considered a differentiated cranial portion of this muscle.
_Relations._--Outer surface with the following, beginning with the caudal end: the sartorius (Fig. 68, _q_), the latissimus dorsi (Fig. 68, _m_), the lumbodorsal fascia (Fig. 68, _y_), the serratus posterior inferior (Fig. 73, _n_) and superior (Fig. 73, _l_), and the levator scapulæ (Fig. 73, _h_). Lateral margin with the abdominal muscles, the iliocostal (Fig. 69, _h_), and the levator scapulæ (Fig. 73, _h_). Medial side with the multifidus spinæ (Fig. 70, _d_), the spinous processes of the thoracic vertebræ, the spinalis dorsi (Fig. 69, _g_), the complexus (Fig. 69, _b_), the biventer cervicis (Fig. 69, _a_), and the longissimus capitis (Fig. 69, _e_).
=M. iliocostalis= (Fig. 69, _h_).--This is a muscle about 1½ to 2 centimeters wide, lying on the dorsal portion of the ribs, laterad of the longissimus dorsi (_f′_). It is composed of many partly separated bundles, each with an oblique tendon. The muscle begins at the last or next to the last rib, where it is connected with the longissimus by a rather small bundle of fibres. The rest of the muscle-fibres take origin in bundles from the lateral surface of the ribs, at about the angles, or from thin tendons connecting the angles, of the ribs; they pass obliquely craniad and are inserted, usually by tendons, on the lateral surface of the third or fourth rib craniad of the one on which the given bundle has origin. The insertions on any given rib lie ventrad of the origins on the same rib. In the cat this muscle is confined to the thoracic region.
_Relations._--Outer surface with the serratus posterior inferior (Fig. 73, _n_) and superior (Fig. 73, _l_), and the levator scapulæ (Fig. 73, _h_). Inner surface with the dorsal surface of the ribs, the external intercostals (Fig. 69, _i_), and craniad with the levatores costarum. Medial edge in contact with the longissimus dorsi (Fig. 69, _f′_).