20 THE AMERICAN MONTHLY [Jan. 



note that they alone compose it, the muscle fibres dis- 

 appearing at the end. Examine single fibres with » 

 high power, and recognize, that they are composed of 

 »ii\\ Bm&lleT fi&rt/lae which run lengthwise in the fibre; 

 that there is a sheath enclosing the fibre, sarcolemma\ that 

 the fibrillae are marked with lines crossing them at equal 

 distances, and that this gives to the fibre a cross-mark- 

 ing, j/n'^i/ow. Directly beneath the sarcolemma there are 

 elongate granular cell-nuclei^ these may not be easily rec- 

 Ojgnized in the glycerine preparation unstained. If sa 

 stain a second preparation before the application of gly- 

 cerine with borax carmine, decolorize with acidulated 

 alcohol and examine small fibres for nuclei, note their 

 exact size and position with reference to the fibre. 



12. The Nervous System. — In dissecting the 'dorsal 

 wall of the body cavity next the spinal column you have 

 probably noted white threads running in the lines be- 

 tween the myotomes outward from the spine, these are 

 the spinal nerves. A pair can be seen at the interval be- 

 tween each two vertebrae through the entire length of 

 ,tli6 trunk, and they are also present in the post-abdomen 

 in the same way, though not there so easily traced; there is 

 thus a metamerism in the nervous system. The kpinal 

 nerves are of approximately the same diameter through- 

 out the series excepting at the levels of the front and 

 hind limbs, where several of them are considerably 

 larger than the rest, this is because ihey ^re com- 

 posed of the additional fibers that go to the muscles and 

 skin of the limbs. How many of these nerves to the 

 limbs do you recognize ? In the head there is a series of 

 cranial nerves which relate the parts of the head with the 

 brain; as in the fish, the spinal canal lodges the spinal 

 ^or^/ which can be seen by removing the neural arclies. 

 There is % sympathetic system but its dissection is very dif- 

 ficult. 



