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. 
/nsertion into the fossa laterad of the condyle of the occipi- 
tal bone. 
Relations.—Ventral surface with the digastric (Fig. 65, 4) 
and the lymphatic gland ventrad of the ear. Dorsal surface 
with the wing of the atlas. 
Action.—F lexes the head laterally. 
M. longus colli (Fig. 65, 2’, g’’).—A long, rather slender 
muscle lying on the ventral surface of the cervical and first six 
thoracic vertebrzee. 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 vertebra. 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 vertebre. These bundles pass craniomediad, so that 
those from the muscles of opposite sides meet and are inserted 
on the centra of the vertebre 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 vertebrz. 
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 with the sternum, corre- 
sponding to the pectoralis muscles of man, fall into a consider- 
