MUSCLES OF THE TRUNK. 263 



2. Attachmmts. — Its aponeurosis, closely united to that of the latissimus 

 dorsi, which covers it, is attached to the spinous processes of the dorsal vertebrse 

 succeeding the tenth, and to some lumbar vertebrae. Its digitations are fixed to 

 the posterior border and external face of the nine last ribs. 



3. Relations. — Outwards, with the latissimus dorsi ; inwards, with the small 

 anterior serratus, the longissimus dorsi, transversalis costarum, and the external 

 intercostals. Some of its posterior digitations are partly concealed by those of 

 the great oblique muscle of the abdomen ; the last, indeed, is entirely covered by 

 that muscle. 



4. Action. — This is an expiratory muscle, in consequence of its drawing the 

 ribs backwards and upwards. 



Third Layer. 

 5. The Ilio-8pinalis Muscle (Longissimus Doesi) (Fig. 163). 



Synonyms. — It represents the loug dorsal, short transversal, and long spinous of Bourgelat. 

 Cuvier and others have described it as consisting generally, in Mammalia, of five particular 

 muscles, designated as longissimus dorsi, transversalis cervicis, semispinalis dorsi, and semi- 

 spinalis colli. It corresponds to the longissimus dorsi, and transversalis cervicis of Man. 



(Percivall designates this important muscle the longissimus dorsi — the name given to its 

 analogue in Man, By Girard, Leyh, and Oliauveau, it is styled the ilio-spinalis.) 



Extent — Situation. — This, the most powerful and complex of all the muscles 

 in the body, extends along the dorso-lumbar spine, above the costal arches, from 

 the anterior border of the ilium to the middle of the cervical spine. 



Form. — It is elongated from before to behind, and flattened above and below 

 in its posterior half, which represents the common mass in Man ; this mass is 

 prismatic in form, thick inwards, and thin outwards. Anteriorly, it is flat on 

 both sides, and bifurcates into two vohmiinous branches, a superior and inferior, 

 between which pass the insertions of the complexus to be fixed into the transverse 

 processes of the first dorsal vertebrae. 



Attachments. — 1. Upon the lumbar border, the external angle and internal 

 smface of the ilium, the sacro-iliac ligament, and the sacrum. 2. To the spinous 

 processes of all the lumbar and dorsal, and last four cervical vertebrae. 3. To 

 the articular tubercles of the lumbar vertebrae and the transverse processes of all 

 the dorsal, and the last fom* cervical vertebrae. 4. To the costiform processes 

 of the lumbar vertebrae, and the external surface of the fifteen or sixteen last ribs. 



Structure. — If this muscle is examined posteriorly, in the part which forms 

 the common mass, it wiU be found to be composed of very compact fleshy fibres, 

 covered in common by a thick aponeurosis. These fibres commence at the 

 posterior extremity of the muscle, and all proceed forward, stopping to make 

 successive insertions on the various bony eminences in its track, and forming 

 three diflferent orders of fasciculi, which are more or less tendinous at their 

 anterior or terminal extremity. These fasciculi are internal and superficial, 

 internal and deep, and external. 



The internal and superficial, or spinal fasciculi, pass to the summits of the 

 spinous processes already noticed when speaking of the attachments. These 

 fasciculi are little, if at all distinct posteriorly ; but they become more so 

 anteriorly. About the sixth dorsal vertebras, they separate from the other 

 fascicuU to form the superior branch of the muscle (Fig. 163, 3). 



The internal and deep, or transverse fasciculi, are those which attach the 

 muscle to the articular tubercles of the lumbar vertebrae and transverse processes 



