132 THE MUSCLES. 



lateral border of the splenius (Fig. 73, b), and sometimes fused 

 with the splenius at its craniad end. It is a cranial continua- 

 tion of the longissimus dorsi (Fig. 69, /"). 



Origin by five slips which are attached by strong tendons 

 to the anterior articular processes of the last four cervical 

 vertebrai. The tendons are common to this muscle and the 

 complexus. The five slips unite to form a flat belly which has 

 its 



Insertion, by a strong rounded tendon into the mastoid 

 process of the temporal bone. The tendon may be closely 

 united to that of the splenius. 



Relations. — Lateral surface with the sternomastoid (Fig. 

 68, c), the levator scapulas (Fig. 73, //), and longissimus dorsi 

 (Fig. 6c), f"). Medial surface with the splenius (Fig. 73, b) 

 (to which it is partly united), the complexus (Fig. 69, b), and 

 the longus atlantis (Fig. 69, d). 



Action. — Lateral flexor of the head. 



M. biventer cervicis (Fig. 69, a) (medial portion of 

 M. semispinalis cervicis et capitis). — The biventer cervicis is 

 aflat muscle which lies beneath the splenius (Fig. 73, /;), next 

 the median line of the neck, with its fibres longitudinal. 



Origin in three or four slips from the surface of the three 

 or four aponeurotic arches which take origin from the tips of 

 the spinous processes of the last cervical and the first three 

 thoracic vertebrae and pass laterad and caudad to the anterior 

 processes of the second, third, fourth, and fifth thoracic verte- 

 brae. These arches are deviated from their straight course by 

 four aponeurotic bands which pass from them obliquely caudad 

 and dorsad to the sides of the spinous processes of the vertebrae 

 into which the arches are inserted. The arches form the 

 beginning of the sheet of fascia which passes outside of the 

 longitudinal supraspinous muscles, and the anchoring bands 

 form the beginning of a similar sheet which passes within the 

 longitudinal supraspinous muscles. An additional slip may 

 take origin from the cervical ligament between the last cervical 

 and the first thoracic vertebrae. The fibres form a flat band 

 divided by two or three oblique tendinous intersections. It 

 adheres closely to the cervical supraspinous ligament. 



