THE MUSCULAR SYSTEM 207 



system innerved by the dorsal branches of the spinal nerves. 

 They lie lodged in the space embraced by the spinous and trans- 

 verse processes of the vertebrae and run in the main in a longi- 

 tudinal direction. They are beset with metameric series of 

 tendons, which attach themselves to the corresponding portions 

 of successive vertebrae or ribs, and plainly suggest a segmental 

 origin. Proceeding inwards from the more superficial series 

 they may be divided as follows, although it must be remem- 

 bered that the muscles are often closely attached to one another 

 and are not as distinct as in most other regions. 



I. SPINO-TRANSVERSALIS SYSTEM. This system, the fibers 

 of which arise from spinous and insert on transverse processes, 

 consists of a single muscle, the splenius, confined to the anterior 

 portion of the trunk, and unrepresented posterior to about the 

 middle of the thoracic vertebrae. In form it is a thin sheet of 

 oblique fibers, a portion of which, splenins cervicis [colli], 

 inserts into the transverse processes of cervical vertebrae, while 

 the remainder, splenius capitis, inserts into the base of the 

 skull. 



II. SACRO - TRANSVERSO - TRANSVERSALIS SYSTEM. This 



arises from a large mass of muscular fibers filling in the space 

 between the hip-girdle and the most posterior ribs. These 

 fibers take their origin from sacrum and ilium, and from the 

 lumbo-dorsal fascia. As the fibers issuing from this origin are 

 not sufficient to supply the entire vertebral column, they are 

 reinforced by others which arise from the transverse processes 

 of the vertebrae, beginning with the lowest lumbar. The 

 metameric insertions' are in two longitudinal ro\vs, or series, 

 the outer into the ribs, and the inner into the transverse pro- 

 cesses. A bundle of the more anterior fibers of the latter 

 inserts into the base of the skull. The system may thus be 

 designated sacro-transverso-transversalis, the first two elements 

 designating the origin, the third, taken in the broad sense and 

 including the ribs, the insertion. 



The outer series begins posteriorly as the sacro-Iumbalis, and 

 becomes continued in the region of the ribs by a series of mus- 

 cular slips arising from lower ribs and inserting in upper, 

 miiscuhts accessorius ad sacro-lumbalem. A still further con- 



