340 ANATOMY OF THE RABBIT 



ly, 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 accessory 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 

 iliocostalis dorsi. Medially, it receives 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 

 serratus anterior, but a number of accessory slips carry the 

 insertion forward to the transverse process of the atlas. 

 This portion is the longissimus cervicis. A separate band 

 of fibres arising chiefly from the transverse processes of 

 the second to fourth thoracic vertebrae joins the lateral, 

 ventral portion of the splenius, and forms the longissimus 

 capitis. It is inserted with the splenius on the mastoid 

 portion of the skull. 



(b) The semispinalis and multifidus. The band of muscle 

 lying between the longissimus and the middle line, is com- 

 posed of partly fused slips, arising for the most part by very 

 long tendons from the mamillary and transverse processes, 

 and inserted forwards on the spinous processes. It is 

 divisible into two portions, which are superficially separated 

 by a constricted area lying at the level of the last thoracic 

 vertebra, this being also the point where the muscle is fused 

 with the longissimus. The anterior portion, the semi- 

 spinalis dorsi, is inserted by a series of fleshy slips on the 

 spinous processes of the more anterior thoracic vertebrae, but 

 extends to the spinous process of the third or fourth cervical 

 vertebra. The posterior portion, the multifidus, increases 



