526 



DISSECTION OF THE BACK. 



offsets to 

 the neck. 



Vessels and 

 nerves. 



Erector 

 spin* is 

 single 

 below, 



divided 

 above ; 



superficial 

 tendon ; 



origin. 



dorsi) from the inner side of the longissimus, and to divide longi- 

 tudinally the part of the thick aponeurosis springing from the 

 lumbar spines, so as to separate the erector from the subjacent 

 multifidus spinae. From the longissimus, as from the ilio-costalis, 

 a fleshy piece (transversalis colli and trachelo-mastoid) is continued 

 into the neck. 



Between the longissimus and the multifidus spinae are th< 

 internal branches of the posterior divisions of the dorsal ant 

 lumbar nerves, with offsets of the intercostal and lumbar vessels. 



ERECTOR SPINES. This is the muscular mass on the side of the 

 spine, extending from the lower part of the sacrum to the head. II 

 is single and pointed below, attains its greatest size in the loins, and 

 over the thorax becomes divided into secondary portions to which 

 the special names are given. Its prolongations to the neck and heat 

 are very slender. On its posterior surface, in the lumbar and sacra 

 regions, is a strong flat tendon of origin, from which most of th( 

 fleshy fibres spring. The muscle arises internally from the lower 

 two or three dorsal, and all the lumbar and sacral spines ; externally 

 from the posterior fifth of the iliac crest at the inner aspect ; ant 

 inferiorly from the lower part of the back of the sacrum. Below 

 the last rib it divides into the ilio-costalis and longissimus dorsi 

 and in the thoracic region the spinalis dorsi is given off fron 

 the inner side of the latter part. 



The ILIO-COSTALIS or SACRO-LUMBALIS is derived from the outer 

 and superficial part of the common mass of the erector in the loins 

 Its fibres end in six or seven tendons, which are inserted into the 

 angles of as many of the lower ribs. It is continued to the uppei 

 ribs and the neck by the two following muscles 



The ACCESSORIUS (musculus accessorius ad ilio-costalern ; fig. 

 190, D) arises by a series of tendinous and fleshy slips from the 

 angles of the lower six ribs internal to the insertion of the ilio- 

 costalis ; and it ends in tendons which are inserted into the remain 

 ing ribs in a line with the ilio-costalis, and into the transverse 

 process of the seventh cervical vertebra. 



The CERVICALIS ASCENDENS is a muscular slip prolonging the 

 accessorius into the neck ; it arises from four ribs, viz., the sixth, 

 fifth, fourth, and third, and is inserted into the posterior tubercles 

 of the sixth, fifth, and fourth cervical vertebrae. 



The LONGISSIMUS DORSI is the largest of the pieces resulting 

 from the division of the erector spinae, and has two sets of 

 insertions into the vertebrae and ribs. Internally it gives off a 

 series of fleshy and tendinous bundles to the accessory processes of 

 the lumbar vertebrae, and the transverse processes of all the dorsal 

 vertebras : externally it is attached by thick fleshy slips to the 

 transverse processes of the lumbar vertebrae, and the middle layer 

 of the fascia lumborum, and by thin flattened processes to the ribs, 

 except the first two or three, between the tuberosity and angle. Its 

 is continued muscular prolongation to the neck is united with the upper fleshy 

 fibres, and splits into the two following pieces : 



The TRANSVERSALIS COLLI (fig. 191, B) arises from the transverse 



Ilio- 

 costalis : 



insertion. 



Acces- 

 sorius : 



origin ; 

 insertion. 



Cervicalis 

 ascendens : 



origin ; 

 insertion. 



Longissimus 

 dorsi : 



double 

 insertion ; 



to neck by 



