PARTS OF THE ERECTOR SPISLE. 525 



small branches from the external divisions of the posterior cervical 

 nerves to the pieces of the muscle are to be looked for. 



As the ERECTOR SPIXJE is displayed in the dorsal and lumbar Define off- 

 regions, two prolongations from it to the cervical vertebrae and the*erector 

 the head are to be defined : One, a thin narrow muscle, the cervi- s P in - 



'/'<, is continued beyond the ribs from the outer piece of 



the erector (ilio-costalis), and is to be separated from the muscles 



around. The other is a larger offset of the inner piece (longissimus 



of the erector muscle ; single at first where it is united with 



the fibres of the longissimus, it is divided afterwards, like the 



splenius, into a cranial part (trachelo-mastoid) and a cervical part 



-'ersalis colli). 



The serratus inferior is to be detached from the spines and Show the 

 thrown outwards, when fine nerves will be found entering it like 

 those to the upper muscle. The superficial layer of the fascia JJ 

 lumboruin is also to be removed, and the areolar tissue is to be 

 cleaned from the surface of the large mass of the erector spinae 

 which now comes into view. Opposite the last rib is an inter- 

 muscular interval, which divides the erector spinae into an outer 

 piece (ilio-costalis), and an inner (longissimus dorsi). By sinking liio- 

 the knife into this interval the ilio-costalis may be turned out- 

 wards, and the longitudinal column of muscle forming the outer 

 part of the erector spince will be defined. 



Its parts are named, from below upwards 



1. The Ilio-costalis. 



2. The Musculus accessorius. 



3. The Cervicalis ascendens. 



The ilio-costalis is a thick mass below, passing on to the lower 

 ribs, and as it is turned outwards the fleshy slips of the accessorius 

 will be uncovered, as they are attached to the angles of the ribs, 

 and from this part its prolongation into the neck as the cervicalis 

 ascendens can be readily made out. In preparing the ilio-costalis Vessels and 

 muscle, the external branches of the dorsal nerves with their nerves - 

 accompanying arteries will appear. 



The attachments of the longissimus dorsi and its prolongation Longissimus 

 upwards as the inner longitudinal column of the erector spince a re dorsi: 

 then to be traced out. 



The parts of this column are named, from below upwards 



1. The Longissimus dorsi. 



2. The Transversalis colli. 



3. The Trachelo-mastoid. 



Externally the longissimus has thin muscular slips of insertion outer 

 into about the lower nine ribs, and thicker processes passing to the 

 transverse processes of the lumbar vertebrae ; the latter may be 

 shown by raising the outer border of the muscle, and clearing away 

 the fat between it and the middle layer of the fascia lumborum. 

 Internally the longissimus is inserted into the transverse processes 

 of the dorsal, and the accessory processes of the lumbar vertebrae by and inner 

 rounded tendons ; and to see these it will be necessary to detach a mser 

 thin tendinous and muscular portion of the erector mass (spinalis spinalis 



