UPPER EXTREMITY AND THORAX, POSTERIOR. 389 



Nerve Supply. The ulnar through the deep palmar 

 branch (the filaments coming from the eighth cervical 

 nerve). 



Action. To extend the second and third phalanges, to 

 flex the first phalanges of the four fingers to which they 



Diag. 25. DIAGRAM OF THE INSERTION OF THE LUMBRICALES AND INTEROSSEI 

 MUSCLES INTO THE APONEUROTIC TENDON OF THE EXTENSOR COMMUNIS DIGI- 

 TORUM, TO ILLUSTRATE THEIR DOUBLE ACTION AS FLEXORS OF THE FIRST PHALANGES 

 AND EXTENSORS OF THE LAST Two SETS OF PHALANGES. (/. S. //,) 



are attached. This action is in common with the palmar 

 set of interossei and the lumbricales. The distinctive action 

 of the dorsal set of muscles is abduction of the fingers 

 from a line through the middle finger. 



THE SPINAL CORD. 



DISSECTION. 



The dissection of the spinal cord is not practicable in the usual dissecting- 

 room subject, for the cord is so soft that its gross structure cannot be deter- 

 mined. 



A perfectly fresh subject that has been injected as soon as received, or a 

 "pickled subject" that has been preserved with a zinc injection and a hard- 

 ening preservative solution, is to be selected. 



If the brain has been removed as previously described, the dissection can 

 be continued by cleaning out all the mass of muscles which fill in the spinal 

 gutters from the base of the skull to the end of the sacrum. Clean the spi- 

 nous processes, laminae, and articular processes, noting the ligaments of these 

 parts of the spine. 



