THE DISSECTION OF THE BACK 167 



Medially, it is attached to the tips of the spines of the lumbar 

 vertebrae and the sacrum ; and laterally it blends with the 

 posterior surface of the middle lamella (Fig. 71). The 

 aponeurosis of origin of the latissimus dorsi and the serratus 

 posterior inferior arise from its posterior surface. 



Dissection. Make a longitudinal incision through the posterior layer of 

 the lumbar part of the lumbo-dorsal fascia, midway between its medial 

 and its lateral borders. At each end of the longitudinal incision make a 

 transverse incision extending from the spine medially to the lateral border 

 of the rounded mass of spinal muscles lying under cover of the fascia. 

 Turn the medial part of the divided fascia towards the median plane, and 

 verify its attachment to the vertebral spines and the supraspinous ligaments. 

 Pull the lateral part aside, and at the lateral border of the mass of posterior 

 spinal muscles it will be found to blend with a deeper layer, the middle 

 lamella. Push the mass of posterior spinal muscles towards the median 

 plane, and follow the middle lamella of the fascia to its attachment. 



The middle lamella is attached medially to the tips of the 

 transverse processes of the lumbar vertebrae; below to the 

 iliac crest, and above to the last rib. Laterally it blends 

 with the posterior and anterior lamellae, and immediately 

 lateral to its line of union with the posterior lamella the 

 internal oblique arises from its posterior surface. To expose 

 it thoroughly the mass of posterior spinal muscles must be 

 pushed medially. 



Dissection. After the middle lamella has been examined divide it 

 longitudinally, close to its attachment to the tips of the transverse processes, 

 and transversely along the line of the iliac crest, and turn it laterally. A 

 considerable part of the posterior surface of the quadratus lumborum 

 muscle will then be exposed. Displace the lateral border of the quadratus 

 lumborum towards the median plane, and the anterior lamella of the 

 lumbar part of the lumbo-dorsal fascia will be brought into view. 



The anterior lamella of the lumbar part of the lumbo- 

 dorsal fascia is attached medially to the anterior surfaces of 

 the roots of the transverse processes of the lumbar vertebrae ; 

 laterally it blends with the fused middle and posterior lamellae 

 to form the common aponeurosis of origin of the transversus 

 abdominis muscle, and it is by means of the three lamellae 

 of the lumbar fascia that the latter muscle arises from the tips 

 of the spines, and the tips and the roots of the transverse 

 processes of the lumbar vertebrae. The upper border of the 

 anterior lamella becomes thickened, and extends anterior to 

 the quadratus lumborum from the last rib to the trans- 

 verse process of the first lumbar vertebra as the arcus 

 lumbo-costalis lateralis (O.T. external arcuate ligament); the 



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