266 Anatomy of the Rabbit. 



prises 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 sacro- 

 spinalis, 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 dorsal 

 surface of the sacrum; mamillary processes of the six pos- 

 terior 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 muLifidus 

 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 thin 

 lateral portion, the iliocostalis or longissimus costarum, 

 and a thick medial portion, the longissimus. The latter 

 receives in the posterior portion of the thorax strong acces- 

 sory bundles from the semispinalis muscle on its medial side, 

 the two muscles being inseparable at this point. 

 The iliocostalis is inserted laterally on the ribs as the ilio- 

 costalis dorsi. It receives medially from the ribs a number 

 of accessory bundles, which are inserted forwards to the 

 seventh cervical vertebra as the iliocostalis cervicis. 

 The longissimus is inserted by broad fleshy bands on the 

 posterior margins of the ribs, medial to the accessory origins 

 of the iliocostalis, this portion of the muscle forming the 

 longissimus dorsi. Continuing to the neck it is inserted 

 on the transverse processes of the three posterior cervical 

 vertebrae, medial to the origin of the cervical portion of the 



