THE THORAX. 



The dissection of the thorax cannot be begun until the thoracic limbs 

 have been removed. Along with the thorax it is convenient to combine 

 the examination of the muscles, &c., of the back and loins. 



Dissection. — The dissector's first duty is the removal of the remains 

 of muscles left behind on the separation of the thoracic limbs from the 

 trunk. In doing this care should be taken not to destroy the various 

 branches of the intercostal and lumbar nerves and vessels. 



The dissection of the aponeurotic tendon of origin of the latissimus 

 dorsi muscle demands special care if the lumbo-dorsal fascia (and origin 

 of the dorsal serratus muscle) is not to be injured. 



The lumbo-dorsal fascia (Fascia lumbodorsalis). — This extensive 

 sheet of deep fascia invests the muscles of the back and loins, but may 

 be easily raised from the underlying longissimus dorsi. Medially it is 

 connected with the supra-spinous ligament and the extremities of the 

 spinous processes of the vertebrae. Caudally it is continuous with the 

 gluteal fascia. In the region of the scapula it develops into a strong 

 sheet, firmly attached to the spinous processes of the third, fourth and 

 fifth thoracic vertebrae, affording origin to the rhomboid and splenius 

 muscles and connected with the scapular attachment of the ventral 

 serratus muscle. Later in the dissection it will be found that the 

 lumbo-dorsal fascia sends a strong septum from its deep face between 

 the longissimus dorsi and ilio-costalis muscles, and a weaker septum 

 between the longissimus dorsi and spinalis muscles. 



Laterally the lumbo-dorsal fascia splits into two layers, the more 

 superficial of which constitutes the aponeurotic origin of the latissimus 

 dorsi muscle. The deeper layer affords origin to the dorsal serratus 

 and ilio-costalis and muscles of the abdominal wall. 



Mm. serrati dorsales. — The two dorsal serratus^ muscles form 

 together a thin sheet extending along the greater part of the dorsal 

 wall of the thorax. Their oricjin is from the lumbo-dorsal fascia, and 

 the muscular bundles succeeding this extensive aponeurotic origin run 

 in different directions in the two muscles. 



^ Serratus (from serra, a saw) [L.], toothed or notched like the edge of a saw. 

 1 



