578 THE MECHANICAL FUNCTIONS. 



seen at s, Fig. 230. It is exceedingly probable, 

 though from the minuteness of the parts it is 

 scarcely possible to obtain ocular demonstration 

 of the fact, that the fibrils of the laminae are 

 formed in a similar manner, by being moulded 

 in still more minute compartments, formed by 

 transverse membranous partitions. 



The proper office of the bulb, after it has sup- 

 plied the materials for the formation of the 

 laminae, is to construct the stem of the feather, 

 and unite the laminae to its sides. For this pur- 

 pose the anterior portion of the bulb deposits on 

 its surface a plate of horny substance, while 

 another plate is formed by the posterior part in 

 the interior of the bulb. Thus the bulb becomes 

 divided into two portions, one anterior and the 

 other posterior. The former of these, after 

 having finished the external plate, proceeds to 

 form the spongy substance, which is to connect 

 the two plates, and the posterior portion of the 

 bulb embraces the inner plate, and gradually 

 folds it inwards till its sides meet at the middle 

 groove along the back of the stem. The anterior 

 part of the bulb, during the process of filling up 

 the stem, exhibits a series of conical shaped 

 membranes, as is seen in the section, Fig. 231 ; 

 the points of the cones being directed upwards, 

 and their intervals being occupied by the spongy 

 substance in different stages of consolidation, 

 and more perfected in proportion as they are 

 situated nearer the apex of the stem. 



