THE USE OF INSTRUMENTS. 201 



pecially needful in the trimming of vessels and nerves and inflated 

 hollow viscera ( 331). 



593. Use of the Forceps ( 145). The forceps are commonly 

 held between the pollex and the index. In long continued dissec- 

 tions the medius may be substituted for the index at intervals. The 

 digits should be employed in place of the forceps when practicable, 

 both as a relief from fatigue and to avoid crushing the tissues. 



The forceps should be used upon muscles as little as possible, 

 and vessels and nerves should be grasped by their sheath of con- 

 nective tissue. For the separation of slender muscles and of vessels 

 and nerves, the safest way sometimes is to insert the tip of the closed 

 forceps and then allow the blades to separate gently. 



594. Use of the Tracer ( 166). The tracer is to be held like 

 a pen or pencil. Its form permits a rotation on its axis, so that the 

 point may have any desired direction. 



The tracer should be more constantly in the hand than any other 

 instrument. Scalpels and other sharp instruments should only be 

 used when the tracer will not answer the purpose. 



The tracer is also very useful in detecting the position of con- 

 cealed hard parts, as ribs, cartilages and vertebrae. The point may 

 be introduced deeply without impairing the condition of the parts for 

 dissection, and the curvature enables one to lift upon it the ribs or 

 cartilages so as to couut them more accurately. 



595. Use of the Arthrotome ( 135). As its name implies, 

 the distinctive use of this instrument is for the division of joints and 

 other rough operations which might injure the more delicate edge 

 of the scalpels. Yet the student should accustom himself to accu- 

 rate and careful manipulation, and endeavor to separate the contig- 

 uous bones at an arthron without injuring the cartilages. He 

 should try to feel with the point of the instrument. 



PRACTICAL SUGGESTIONS FOR DISSECTORS. 



596. 1. Select a lean animal for all anatomical purposes, and 

 especially for the dissection of the muscles, vessels and nerves. The 

 directions for 'killing are given in 192. 



2. Take the precautions for cleanliness which are described in 

 199. 



3. Remove superfluous parts of the animal, the tail in some cases 

 ( 243), the caudal or cephalic region of the body, according to the 



