_Origin_ from the cranial border of the first costal cartilage. The muscle passes craniad closely united near its caudal end to the sternothyroid (_g′_). _Insertion_ (Fig. 67, _m_) into the outer half of the ventral surface of the body of the hyoid bone caudad of the origin of the geniohyoid (Fig. 67, _g_). _Relations._--Outer surface with the sternomastoid (Fig. 65, _g_). Inner surface with the thyrohyoid (Fig. 65, _f_; Fig. 67, _p_), the trachea (Fig. 67, 4), and the larynx. _Action._--Draws the hyoid caudad. Raises the ribs and sternum when the hyoid is fixed. =M. sternothyreoideus= (Fig. 65, _g′_).--The sternothyroid lies beneath the sternohyoid and is connected with it at its caudal end. _Origin_ from the first costal cartilage beneath the sternohyoid. _Insertion_ (Fig. 67, _o_) into the lateral part of the caudal border of the thyroid cartilage of the larynx. _Relations._--Outer surface with the sternohyoid (Fig. 65, _e_) and laterally with the sternomastoid (Fig. 65, _g_). Inner surface with the trachea (Fig. 67, 4), and at the lateral edge with the thyroid gland (Fig. 67, 6). _Action._--Pulls the larynx caudad. =M. scalenus= (Fig. 73, _f_-_f‴_).--This is a large and complex muscle lying on the ventral side of the neck and the lateral surface of the thorax. It might equally well be classified with the muscles of the thorax. It is divisible into a considerable number of interconnected bundles which are sometimes described as separate muscles. The largest, middle portion (=scalenus medius=) (_f′_) takes origin by thin tendons from the sixth, seventh, eighth, and ninth ribs, just dorsad of their junction with the cartilages; these tendons unite near their origins to form a flat band which becomes fleshy at about the fifth rib, passes craniad, and unites just craniad of the first rib with the other parts of the muscle. The dorsal portion (=scalenus posterior=) (_f″_) has origin by a very slender tendon from about the middle of the outer surface of the third or fourth rib; it extends craniad as a narrow band which passes laterad between the heads of the serratus anterior (_i_) that are attached to the second and third (or third and fourth) ribs, and unites with the other heads. The ventral head (part of =scalenus anterior=) (_f‴_) arises by one or two minute tendons from the cartilages of the second and third ribs; they are partly united with the transversus costarum (_j_). This ventral head passes craniad and unites with the other heads. These three divisions unite just craniad of the first rib with each other and with the cervical portion of the muscle (_f_) (part of =scalenus anterior=). This consists of a number of small bundles of fibres which arise from the first rib and the transverse processes of the first thoracic and the last six cervical vertebræ.