576 THE MECHANICAL FUNCTIONS. 



approach one another at the lower part of the 

 stem, till they meet at a pomt, where the longi- 

 tudinal groove terminates, and where there is a 

 small orifice (o), leading to the interior of the 

 quill. From this part the transparent tubular 

 portion of the quill (t) commences ; and at its 

 lower extremity (l) there exists a second, or lower 

 orifice. 



The entire organ which forms the feather, and 

 which may be termed its matrix, is represented 

 in Fig. 229, when it has attained the cylindric 

 form already described ; of which a is the apex, 

 or conical part that rises above the cuticle, and 

 B the base, by which it is attached to the corium, 

 or true skin. A \\ hite line is seen running lon- 

 gitudinally the whole length of the cylinder, and 

 another, exactly similar to it, is met with on the 

 opposite side : the one corresponds in situation 

 to the front, and the other to the back of the 

 stem of the future feather. On laying open the 

 matrix longitudinally, as is shown in Fig. 230, it 

 is found to be composed of a sheath or capsule, 

 and of a central pulpy mass, termed the bulb. 

 The capsule consists of several membranous 

 layers (c, e, s, i), which are more consolidated 

 near the apex, and become gradually softer and 

 more delicate, as we trace them towards the base 

 of the matrix, where their formation is only be- 

 ginning to take place. 



The laminae and their fibrils, the assemblage 



H 



