180 Anatomy of the Rabbit. 



XII. THE VERTEBRAL AND OCCIPITAL MUSCULATURE. 



Dissection on the dorsal surface of the body from the occiput back- 

 ward; also on the lateral and ventral surfaces of the neck. 



The serratus posterior muscle lies on the dorsolateral surface of the 

 thorax. It arises from the ligamentum nuchae and from the lumbo- 

 dorsal fascia back to the last rib, and is inserted on the lateral surfaces 

 of the eight posterior ribs. 



The splenius muscle is a somewhat triangular sheet arising from the 

 ligamentum nuchae and inserted on the supraoccipital and mastoid 

 portions of the skull, extending also to the transverse process of the 

 atlas. 



These two muscles should be divided, the serratus posterior being removed 

 from the surface. 



1. The long muscles of the vertebral column. 



Apart from the iliopsoas, psoas minor, and quadratus lumborum — 

 muscles of appendicular insertion lying on the ventral surface of the 

 vertebral column — the vertebral musculature comprises chiefly modified 

 segmental muscles lying on the dorsal surface, for the most part in the 

 area enclosed by the spinous and transverse processes of the vertebrae. 

 They include the sacrospinalis, semispinalis, and intertransversarii. 

 Their insertions are extended in part laterad to the ribs. In the cervical 

 region they are represented by short muscles, separated for the most 

 part from the thoracic and lumbar portions, and arising by accessory 

 bundles from the anterior ribs, the corresponding thoracic, and the 

 posterior cervical vertebrae. In the cervical region the muscles are 

 easily separated from one another, but in the posterior part of the body 

 it is necessary to dissect away the tough investment of lumbodorsal 

 fascia which covers them. 



(a) The sacrospinalis. Origin: Crest of the ilium and medial 

 surface of the iliac wing; mammillary processes of the six 

 posterior lumbar vertebrae; investing lumbodorsal fascia. 

 This muscle is the largest and strongest muscle of the body. It 

 extends forward over the surfaces of the ribs. Its medial 

 border is separated from the middle line by a space of con- 

 siderable width, in which the semispinalis and multifidus 

 muscles are accommodated. In the lumbar region -it is 

 inserted in a continuous mass on the long transverse processes 

 of the vertebrae and in the interspaces. In the thoracic 

 region the muscle divides into two portions, namely, a slender 

 lateral portion, the iliocostalis, and a thick medial portion, 

 the longissimus. The latter receives in the posterior portion 

 of the thorax strong accessory bundles from the semi- 

 spinalis muscle on its medial side,* the two muscles being 

 inseparable at this point. 



