124 THE MUSCLES. 



which have been differentiated from this mass. In the greater 

 part of its extent, however, it is possible to distinguish only 

 more or less closely interconnected bundles, — the more clearly 

 marked of which have received special names. 



The great dorsal mass running along each side of the 

 vertebral column, occupying the space between the spinous 

 processes and the transverse processes, receives the general 

 name of M. extensor dorsi communis ; the separate muscles 

 are to be considered as parts or differentiations of this. The 

 largest part of the mass is in the lumbar region (first portion 

 of the longissimus dorsi, Fig. 69, /). At the caudal end of 

 the thorax a lateral mass, parts of which become connected 

 with the ribs, is separated off from the main part of the 

 muscle; this extends craniad into the cervical region as 

 M. iliocostalis (//). The main portion of the longissimus dorsi 

 (/') continues craniad on the medial side of the iliocostal into 

 the neck region. At about the level of the eighth or ninth 

 thoracic vertebra a strip begins to become separated off on the 

 medial side of the longissimus ; further forward it becomes 

 clearly distinct, forming the spinalis dorsi (j^). The separate 

 muscles connecting the cervical vertebr.ne with each other and 

 with the head are differentiations of the extensor dorsi com- 

 munis. 



A still deeper set of fibres, interconnecting the vertebrae, 

 forms the multifidus spinas and a number of other small 

 muscles. 



A description of the different bundles of fibres, under the 

 names usually given, follows. Certain general principles are 

 observed in some of the names used. Muscles which intercon- 

 nect the spinous processes of the vertebrae receive the name 

 spinalis. Those interconnecting contiguous spinous processes 

 are called interspinalis. Muscles attached at one end to 

 transverse processes, at the other to the spinous processes, 

 receive the name transversospinalis. Semispinalis has the 

 same signification as transversospinalis, but is a name usually 

 applied to subdivisions of the transversospinalis group. The 

 intertransversarii are muscles interconnecting the transverse 

 processes. 



