_Relations._—Anteriorly the posterior border of the vertebræ in front and posteriorly the anterior border of the succeeding vertebræ, inferiorly by the vertebræ. _Action._—To approximate the spinous portion of the vertebræ. =Interarticulares= (Fig. 17, No. _A_, 4). _Location._—Supero-laterally to the vertebræ. Between the postzygapophysis. _Origin and Insertion._—From the posterior margin of the ring of the atlas to the postzygapophysis of the axis. Then in the succeeding vertebræ from the postzygapophysis of the vertebra to the same of the succeeding vertebra. _Shape._—Muscular bundle. _Relations._—Inferiorly with the vertebræ. Supero-laterally with the obliquo-transversales. _Action._—Aids in approximating the vertebræ in a supero-lateral direction. =Obliquo-transversales= (Fig. 17, _A_, No. 1). _Location._—Supero-lateral to the vertebræ. _Origin and Insertion._—Passes obliquely from the transverse process of one vertebra to the postzygapophysis of the vertebra beyond. _Shape._—A thin fasciculus. _Relations._—Inferiorly with the interarticulares and laterally with the intertransversales. _Action._—Aids in flexing the vertebræ supero-laterally. =Intertransversales= (Fig. 19, No. 12). _Location._—Laterally to the vertebræ. _Origin and Insertion._—Extend between the transverse processes beginning at the third cervical vertebra. _Shape._—Short, thick. _Relations._—Laterally the vertebræ. Superiorly the obliquo-transversales. _Action._—Aids in flexing the vertebræ laterally. =Scalenus Medius= (Fig. 19, No. 18). (Synonym.—Scalenus.) _Location._—Supero-laterally to the entrance of the thorax. _Origin._—From the diapophysis and pleurapophysis of the eleventh cervical vertebra. _Insertion._—To the entire border of the first rib. A few fibers pass over to the anterior free margin of the middle third of the second rib. _Shape._—Rather pyramidal in shape with base uppermost. _Relations._—Posteriorly with the levatores costarum. Internally with the longus colli. _Action._—When the first rib is fixed singly, turns the neck to one side; acting with its fellow, extends the neck. When the neck is fixed, by drawing the first rib forward, it acts as an inspiratory muscle. THE MUSCLES OF THE AIR PASSAGES The Superior Larynx Constrictor glottidis Thyreo-arytenoideus The Inferior Larynx Tracheo-lateralis Broncho-trachealis posticus Broncho-trachealis anticus Broncho-trachealis brevis Bronchialis posticus Bronchialis anticus Sterno-trachealis =Constrictor Glottidis.= _Location._—Supero-anterior portion of the superior larynx. _Origin._—From the superior and longitudinal line of the thyroid plate.