On the left side the longus capitis and one head of the levator scapulæ ventralis have been cut, in order to show the rectus capitis anterior minor. _a_, M. longus capitis; _b_, M. rectus capitis anterior minor; _c_, M. levator scapulæ ventralis (_c′_, its atlantal head; _c″_, its occipital head); _d_, M. rectus capitis lateralis; _e_, M. obliquus capitis superior; _f_, M. longissimus capitis; _g_, M. longus colli (_g′_, its cervical portion; _g″_, its thoracic portion); _h_, part of M. scalenus. 1, bulla tympani; 2, ventral atlanto-occipital membrane; 3, ventral arch of atlas; 4, first rib.] =M. rectus capitis lateralis= (Fig. 72, _d_).--This lies ventrad of the obliquus superior (_e_) on the ventral face of the transverse process of the atlas and at first appears to be a part of the obliquus superior. _Origin_ from the median half of the ventral surface of the transverse process of the atlas. The fibres form a cylindrical mass which passes craniad and slightly laterad. _Insertion_ into the fossa laterad of the condyle of the occipital bone. _Relations._--Ventral surface with the digastric (Fig. 65, _b_) and the lymphatic gland ventrad of the ear. Dorsal surface with the wing of the atlas. _Action._--Flexes the head laterally. =M. longus colli= (Fig. 65, _g′_, _g″_).--A long, rather slender muscle lying on the ventral surface of the cervical and first six thoracic vertebræ. It consists of many separate bundles, and is divisible into a thoracic and a cervical portion. The =thoracic portion= (_g″_) has origin by six heads from the ventral surface of the first six thoracic vertebræ. The separate heads join to form a band which passes craniad and is inserted for the most part into the processus costarius of the sixth cervical vertebra; a portion of it joins the cervical division of the muscle. The =cervical portion= (_g′_) is a continuation craniad of the thoracic portion. It arises in small bundles from the transverse processes and sides of the ventral surfaces of the centra of the cervical vertebræ. These bundles pass craniomediad, so that those from the muscles of opposite sides meet and are inserted on the centra of the vertebræ in the middle line, each pair of bundles forming a V opening caudad. The most cranial insertion is into the tubercle on the middle of the ventral surface of the ventral arch of the atlas (3). _Relations._--Dorsal surface with the centra of the vertebræ. Ventral surface in the thorax with the trachea; in the neck with the œsophagus. Medial edge with the muscle of the opposite side. Lateral margin in the cervical region with the longus capitis (_a_). _Action._--Bends the neck. 3. =Muscles of the Thorax.= A. BREAST-MUSCLES (connecting the arm and thorax) (Fig. 65, page 109).