128 THE MUSCLES 



most of the fibres are inserted in separate bundles by small 

 tendons on the transverse processes of the vertebrae, while 

 some of the medial fibres unite with tendinous strands which 

 become attached to the laminae and articular processes of the 

 vertebrae. At the region of the eighth or ninth thoracic verte- 

 bra the spinalis dorsi (Fig. 69, g) begins to be separated off 

 on the medial side, the separation becoming complete only 

 some distance farther craniad ; the longissimus dorsi then con- 

 tinues into the cervical region (/""). Bundles of fibres become 

 attached in the manner above described to transverse processes 

 of all the thoracic vertebrae. In the cervical region (/"} the 

 muscle spreads out and becomes thinner, and bundles of fibres 

 become attached to the transverse processes of the cervical 

 vertebrae as far forward as the second. In the more cranial 

 portion of its extent the muscle receives fibres having origin on 

 the articular processes and laminae of the cervical and a few of 

 the more cranial thoracic vertebrae. 



The portion of the muscle which is inserted on the cervical 

 transverse processes (f"} is sometimes distinguished as the 

 longissimus cervicis; it is not well separated from the rest of 

 the muscle in the cat. The longissimus capitis (Fig. 69, c; 

 Fig- 73, g} is to be considered a differentiated cranial portion 

 of this muscle. 



Relations. Outer surface with the following, beginning 

 with the caudal end: the sartorius (Fig. 68, ^), the latissimus 

 dorsi (Fig. 68, ;//), the lumbodorsal fascia (Fig. 68, _^), the 

 serratus posterior inferior (Fig. ^3, ;/) and superior (Fig. 

 73, /), and the levator scapulae (Fig. 73, Ji). Lateral margin 

 with the abdominal muscles, the iliocostal (Fig. 69, //), and 

 the levator scapulae (Fig. 73, Ji). Medial side with the multi- 

 fidus spinae (Fig. 70, </), the spinous processes of the thoracic 

 vertebrae, the spinalis dorsi (Fig. 69, g}, the complexus (Fig. 

 69, b], the biventer cervicis (Fig. 69, a), and the longissimus 

 capitis (Fig. 69, e). 



Action. Extends the vertebral column. 



M. iliocostalis (Fig. 69, Ji]. This is a muscle about \\ 

 to 2 centimeters wide, lying on the dorsal portion of the ribs, 

 laterad of the longissimus dorsi (f). It is composed of many 



