144 THE MUSCLES. 



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, 



bisertion into the fossa laterad of the condyle of the occipi- 

 tal 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 vertebrae. 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 vertebrae. 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 (^') 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 vertebrae. These bundles pass craniomediad, so that 

 those from the muscles of opposite sides meet and are inserted 

 on the centra of the vertebrai 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 sur- 

 face of the ventral arch of the atlas (3). 



Relations. — Dorsal surface with the centra of the vertebras. 

 Ventral surface in the thorax with the trachea; in the neck 

 with the CEsophagus. 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 (con- 

 necting the arm and thorax) (Fig. 65, page 109). 



The muscles connecting the arm \\\\\\ the sternum, corre- 

 sponding to the pectoralis muscles of man, fall into a consider- 



