NERVOUS TISSUES ANE SYSTEMS. 89 



places. The bulbs vary in shape, round to cylindrical, and consist 

 of a fibrous capsule and a central core in which terminates an axis 

 cylinder. The Pacinian corpuscle, which occurs in the subcutaneous 

 tissue of certain localities, is a variety of the same and is peculiar in 

 exhibiting many concentric fibrous Iamina3. 



Touch, corpuscles occur in the papillae of the skin. The nerve 

 fibre as it enters the corpuscle breaks up into fibrils, which form a 

 coil, giving a striated appearance. 



3. Nemo-epithelium. This occurs in the perceptive organs and 

 consists of highly specialized cells, such as the rod and cone cells of 

 the retina, and olfactory and gustatory cells. These cells receive 

 the stimuli from external sources, the nerve-fibres conveying them 

 onward to the. nerve centers. 



Laboratory exercise No. 24. The spinal cord. Harden pieces of the 

 spinal cord of a cat in Muller's fluid, embed in paraffin, and stain with 

 hsematoxylin and eosin, method No. 8. Examine first with L. P., then 

 with H. P. Study the structure of the inclosing membranes. Observe 

 the septa of connective tissue extending- from the pia mater into the 

 underlying tissue. Find the posterior median septum, and the anterior 

 median fissure. How can you always distinguish the posterior from 

 the anterior surface of the cord? Note the difference in appearance 

 between the white matter and gray matter. Make a study of the white 

 matter, noting the axis cylinders with their medullary sheaths. Find 

 the posterior and anterior lateral columns. Make a study of the gray 

 matter, observing the anterior and posterior lateral cornua. Look for 

 the anterior and posterior roots of the spinal nerves. Observe the cen- 

 tral commissure inclosing the central canal. Multipolar ganglion cells 

 should be found in the gray matter. Follow out an axis cylinder until 

 it enters the white matter. Look for neuroglia. Drawings. 



Laboratory exercise No. 25. The cerebrum. Harden in Muller's fluid, 

 embed in paraffin, and stain with ha3matoxylin and eosin, method No. 8. 

 In examining the cerebrum, search first for the pia mater; then demon- 

 strate the cerebral cortex with its five layers made up of cells of differ- 

 ent forms and sizes; and, finally, the medulla, consisting chiefly of me- 

 dullated fibres. The layers of the cerebral cortex, beginning externally, 

 will be arranged in the following order: Granular layer, layer of small 

 pyramidal cells, layer of large pyramidal cells, layer of polymorphous 

 cells, and the layer of fusiform cells. Demonstrate the axis cylinders 

 and their collaterals; observe the bundles of medullary fibres extend- 

 ing between the cells. Drawings. 



Laboratory exercise No. 26. The cerebellum. Harden in Muller's 

 fluid, embed in paraffin, and stain with haBmatoxylin and eosin, method 



