803 AJVATOMICAL TECHNOLOGY. 



directions for albdominal and thoracic transection which are given 



in §§ 237, 242. 



4. See that all the instruments, materials and books for dissec- 

 tion, reference and record are at hand and in order before getting 

 the subject or beginning to work. 



5. Refer constantly to a skeleton, or to the bones especially con- 

 cerned, or to accurate figures. 



6. Have plenty of ligTit upon the part under dissection, so that 

 details of structure may be seen. 



7. When a part from which or toward which an incision is to be 

 carried lies upon the meson, the incision should extend 1-2 cm. 

 beyond the meson. This permits the flap of skin to be reflected 

 across the meson to that extent. If, however, this flap of skin is to 

 be removed, the incision removing it should run parallel with the 

 meson, and upon the side under examination. 



Ohjections to Mesal Incisions. — Botli the ectal and ental aspects of the skin present spe- 

 cial features at some mesal points, and several muscles besides those of the skin itself arise 

 at the meson, and are liable to injury by a mesal incision. There are two sides, presuma- 

 bly similar, but there is only one meson. 



8. Incisions should be as long as may be consistently with the 

 shape and structure of the parts, and the dissector's knowledge of 

 them. 



9. When important or delicate parts are liable to be injured, the 

 cuts should be shorter and more carefully made. 



10. Vessels and nerves should be dissected from the center 

 toward the periphery, so as to avoid the risk of missing, cutting or 

 tearing the branches. 



11. Vessels injected with plaster should be divided with the 

 arthrotome or the bone scissors. 



12. In place of the block, especially while the separated arm is 

 under dissection, a folded wet towel may be used ; this permits a 

 kind of bed to be made which keeps the arm in place. 



13. " To put any group of muscles on the stretch, put the parts 

 concerned in the position into which they would be brought by 

 their antagonistic muscles. For example, to put the flexors of the 

 manus on the stretch, put the manus in a state of extension, and 

 mce versaP — Heath (Keen), A, 16. 



14. Study the actions of a muscle by pulling it in the line it nat-. 

 urally occupies. Note the difference between a direct and an indi- 

 rect action. (Wilder, 4.) 



