208 THE MUSCLES. 



the external fasciculi, go to form. From profound, they now become 

 superficial ; and they are seen springing up between the others, which 

 appear to separate to allow them to pass (Fig. 106, 4, 4). 



The external, or costal fasciculi, turn a little outwards to reach the ribs 

 and costiform processes of the lumbar region ; they are not very apparent 

 in this direction (Fig 106, 2, 2). 



It will be easily understood that all these fasciculi do not come from 

 the common mass, which would be expended long before its termination at 

 the neck, in consequence of the successive emissions of the fasciculi 

 composing it. To prevent this expenditure, there are continually added to 

 it numerous reinforcing bundles of fibres, which arise either from its 

 aponeurotic envelope, or from the bones on whicK the primary fasciculi 

 terminate, and comport themselves absolutely like these, which they are 

 charged to continue to the neck. 



Relations. The ilio-spinalis is covered by the pyramidal point of the 

 principal gluteal muscle, which it receives in a particular excavation, and by 

 the aponeurosis of the great dorsal and the small serrated muscles. It 

 covers the intertransversales of the lumbar region, the transversales of the 

 back and loins, the supercostals (levatores costarum) and the external 

 intercostals. Outwards, it is bordered by the common intercostal. 



The superior branch is covered by the great com plexus and the trans- 

 versales colli. Inwardly, it responds to the cervical ligament and the analo- 

 gous branch of the opposite muscle. 



The inferior branch responds, outwardly, to the angularis of the scapula ; 

 it covers some intertransversales colli, and the aponeurotic digitations which 

 attach the great complexus to the transverse processes of the first dorsal 

 vertehrae. From these digitations it even detaches a number of muscular 

 fasciculi, which go to strengthen this branch of the ilio-spinalis. 



Action. It is a powerful extensor of the vertebral column, which, when 

 it acts singly, it inclines to one side. It may also take part in expiration. 



6. Common Intercostal Muscle. (Fig. 106, 5.) 



Synonyms. Trachelocostalis Girard. The sacro-lumbalis of Man. (Transversalis 

 costarum Percivall.) 



Form Situation. A long, narrow, and thin muscle particularly at its 

 extremities situated along the external border of the preceding muscle, 

 with which it is confounded behind the last rib. 



Structure Attachments. This muscle, whose structure has been com- 

 plicated at will by so many anatomists, is yet extremely simple. It is formed 

 of a series of fasciculi, directed obliquely forwards, downwards, and out- 

 wards, tendinous at their extremities, and originating and terminating 

 successively on the external surface of the ribs, The most posterior leave 

 the external border and inferior face of the common mass. The tendinous 

 digitation of the anterior fasciculus is inserted into the transverse process 

 of the last cervical vertebra, in common with the inferior branch of the ilio- 

 spinalis. 



Relations. Outwards, with the great and small serratus ; inwards, with 

 the external intercostals. 



Action. It depresses the ribs, and may extend the dorsal portion of the 

 spine. 



