MUSCLES OF THE TRUNK. 265 



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 (%. 163, 2, 2). 



It win 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 exhaustion, there are continually added to it numerous bimdles of 

 fibres, which arise either from its aponeurotic envelope, or from the bones on 

 which the primary fasciculi terminate, and comport themselves absolutely like 

 these, which they are charged to continue to the neck. 



Relations. — It is covered by the pyramidal point of the principal gluteal 

 muscle, which it receives in a particular excavation, and by the aponeurosis of 

 the latissimus dorsi and the small serrated muscles. It covers the inter- 

 transversales of the lumbar region, the semispinalis of the back and loins, the 

 levatores costarum, and the external intercostals. Outwards, it is bordered by 

 the transversalis costarum. 



The superior branch is covered by the complexus and the semispinaHs colli. 

 Inwardly, it responds to the cervical ligament and the analogous 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 complexus to the transverse processes of the first dorsal vertebrse. From 

 these digitations it even detaches a number of muscular fasciculi, which go to 

 strengthen this branch of the longissimus dorsi. 



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 Inteecostal Muscle (Teansversalis Costaeum (Fig. 163, 5). 



Synonyms. — Trachelo-coatalis — Girard. The sacro-lumhalis of Man. 



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, the structure of which has been 

 complicated by so many anatomists, is yet extremely simple. It is formed of 

 a series of fasciculi, directed obliquely forwards, downwards, and outwards, 

 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 longissimus dorsi. 



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. 



Fourth Layer. 



Transverse Spinous Muscle of the Back and Loins (Semispinalis 



OF THE Back and Loins) (Fig. 161, 3). 



Synonyms. — Transverso-spinous — Girard. Dorso-lumbar portion of the semispinalis of Maa 

 (The spinalis and semispinalis dorsi — Percivall.) 



Situation — Extent. — This is a very long muscle, directly applied to the super- 



