5o8 



HUMAN ANATOMY. 



Psoas magnus 

 Lumbar vertebra 



Subperitoneal tissue 



Fascia Peritoneum 



The deep fascia of the back invests all the muscles of the dorsal group, 

 separating them from the spino-humeral group. Above, the fascia is not especially 

 strong, and in the cervical arid upper thoracic regions forms what is termed the 

 fascia nuchae, which lies beneath the trapezius and rhomboid muscles. In the lower 

 thoracic and lumbar regions, however, the fascia becomes considerably thickened, 

 especially that portion which invests the sacro-spinalis {vertebral aponeurosis') , form- 

 ing a strong rhomboidal sheet extending from about the level of the sixth thoracic 

 vertebra to the tip of the sacrum, its anterior borders giving attachment to various 

 muscles, while the posterior ones are attached to the posterior portions of the iliac 



crests, where it becomes contin- 

 FiG. 519. uous with the fascia lata covering 



the gluteal muscles. 



This dense layer is termed 

 the fascia lumbo-dorsalis (Fig. 

 559), and is generally regarded 

 as consisting of two lateral por- 

 tions which are practically united 

 in the mid-dorsal line by their 

 common attachment to the spi- 

 nous processes of the vertebrae 

 and the supraspinous ligaments. 

 Each of these lateral portions is 

 again considered as consisting 

 of two layers which together 

 invest the sacro-spinalis (Fig. 

 519), the posterior layer being 

 that which has already been described, while the anterior layer is attached medially 

 to the tips of the transverse processes of the lumbar vertebrae, above to the lower 

 border of the twelfth rib, and below to the crest of the ilium. It passes outward 

 beneath the sacro-spinalis, separating it from the quadratus lumborum, and at the 

 outer border of the former muscle it fuses with the posterior layer to form a strong 

 aponeurotic band, from which the latissimus dorsi and the internal oblique and trans- 

 verse abdominal muscles take partial origin, and which is continued ventrally over 

 the inner surface of the transversus abdominis as \\\^& fascia transvcrsalis. 



Transversalis fascia 



Transversalis muscle 

 Internal oblique 

 External oblique 



Triangle of Petit 

 uadratus lumborum 



Latissimus dorsi 

 Ant. layer of lumbo-dorsal fascia 



Superficial fascia 

 Lumbar spine Posterior layer of lumbo-dorsal fascia 



Skin Sacro-spinalis 



Diagram showing formation and relations of lumbo-dorsal fascia 

 to muscles of body-wall. 



1 



(«) THE TRANSVERSO-COSTAL TRACT. 



1. Sacro-spinalis. 



2. Ilio-costalis. 



3. Longissimus. 



4. Splenius. 



I. Sacro-Spinalis (Fig. 520). 



Attachments. — The sacro-spinalis, sometimes termed the erector spina, forms 

 a large muscular mass occupying the lumbar portion of the vertebral groove. It 

 takes its origiji from the under surface of the lumbo-dorsal fascia, the crest of 

 the ilium, the posterior surface of the sacrum, and the spines of the lumbar ver- 

 tebrae. Anteriorly it divides into three separate muscles, two of which, the ilio- 

 costalis and the longissimus, belong to the transverso-costal group, while the third, 

 ihe spinalis, is a member of the transverso-spinal series. 



Nerve-Supply. — The posterior divisions of the lunibar nerves. 



2. Ilio-Costalis (Fig. 520). 



Attachments. — The ilio-costalis, also termed the sacro-lumbalis, is the most 

 lateral of the three muscles into which the sacro-spinalis divides, and is the forward 

 continuation of the portion of that muscle which arises from the crest of the ilium. 

 The muscle is continued upward in the vertebral groove immediately internal to the 

 angles of the ribs as far as the fourth cervical vertebra, receiving, however, acces- 

 sions from the ribs as it passes over them. The fibres which arise from the iliac 



