FOURTH LAYER. 203 



versalis abdominis, which separates it from the quadratus lumborum ; 

 (in the dorsal region) Avith the multifidus spinae, semi-spinalis dorsi, 

 levatores costarum, intercostal muscles, and ribs as far as their angles. 

 Internally or mesially with the multifidus spinae, and semi-spinalis 

 dorsi, which separate it from the spinous processes and arches of the 

 vertebra?. 



The two layers of aponeurosis of the transversalis abdominis, toge- 

 ther with the spinal column in the lumbar region, and the vertebral 

 aponeurosis with the ribs and spinal column in the dorsal region, form 

 a complete osseo-aponeurotic sheath for the erector spins. 



The CERVICALIS ASCENDENS is the continuation of the sacro-lumbalis 

 upwards into the neck. It arises from the angles of the four upper 

 ribs, and is inserted by slender tendons into the posterior tubercles of 

 the transverse processes of the four lower cervical vertebrae. 



Relations. By its superficial surface with the levator anguli sca- 

 pulae ; by its deep surface with the upper intercostal muscles and ribs, 

 and with the intertransverse muscles; externally with the scalenus 

 posticus; and internally with the transversalis colli. The tendons of 

 insertion are interposed between the attachments of the scalenus pos- 

 ticus and transversalis colli. 



The TRANSVERSALIS COLLI would appear to be the continuation 

 upwards into the neck of the longissimus dorsi ; it arises from the 

 transverse processes of the third, fourth, fifth, and sixth dorsal verte- 

 bra, and is inserted into the posterior tubercles of the transverse pro- 

 cesses of the four or five inferior cervical vertebrae. 



Relations. By its superficial surface with the levator anguli sca- 

 pulae, splenius and longissimus dorsi. By its deep surface, with the 

 complexus, trachelo-mastoideus and vertebrae; externally with the 

 musculus accessorius ad sacro-lumbalem, and cervicalis ascendens ; 

 internally with the trachelo-mastoideus and complexus. The tendons 

 of insertion of this muscle are interposed between the tendons of inser- 

 tion of the cervicalis ascendens on the outer side, and of origin of the 

 trachelo-mastoid on the inner side. 



The TRACHELO-MASTOID is likewise a continuation upwards from 

 the longissimus dorsi. It is a very slender and delicate muscle, arising 

 from the transverse processes of the four upper dorsal and four lower 

 cervical vertebrae, and inserted into the mastoid process to the inner 

 side of the digastric fossa. 



Relations. The same as those of the preceding muscle, excepting 

 that it is interposed between the transversalis colli and the complexus. 

 Its tendons of attachment are the most posterior of those which are 

 connected with the posterior tubercles of the transverse processes of 

 the cervical vertebrae. 



The COMPLEXUS is a large muscle, and with the splenius forms the 

 great bulk of the back of the neck. It crosses the direction of the 

 splenius, arising from the transverse processes of the four upper dor- 

 sal, and from the transverse and articular processes of the four lower 

 cervical vertebrae, and is inserted into the rough surface on the occipital 



