32 THE FROG 
observe that the outermost layer (stratum corneum) is composed 
of extremely flattened cells. This is the horny layer, described 
above, which is periodically shed. The inner or Malpighian 
layer is composed of several layers of cells; the innermost of 
these consists of columnar cells; the other layers show transitional 
stages between the latter and the stratum corneum. 
2. The cutis is composed mainly of connective tissue in which 
are embedded numerous glands; it is roughly divisible into the 
following three layers: 
(a) The outer layer, composed mainly of loose connective tissue, 
contains considerable pigment especially next to the Malpighian 
layer. Between and above the branched cells containing black 
pigment observe the golden pigment cells, which are oval granular 
cells containing, in life, the yellow pigment which gives the golden 
color to the skin. 
The glands are mainly confined to this layer. Each gland is 
flask-shaped and its body is lined by a layer of thick secreting 
epithelial cells. If the section is cut near the middle of the gland 
the neck may be seen extending through the epidermis to the 
surface; the cells of the neck are flattened but they form a layer 
continuous with the secreting cells of the gland. The glands are 
of two kinds, the numerous small mucus glands, and the large 
poison glands, much fewer in number. The poison glands are 
distinguished by their granular contents. 
(b) The middle layer is composed mainly of a compact mass 
of connective tissue fibers which run in a wavy course parallel 
to the surface of the skin. At intervals, transverse bands of 
connective tissue fibers cross this layer and extend into the outer 
layer. Both outer and middle layers are occasionally traversed by 
small bundles of non-striated muscle fibers extending between the 
glands. 
(c) The inner layer is comparatively thin and composed of a 
loose meshwork of connective tissue and blood vessels. This 
layer is connected only at wide intervals with a similar layer of 
connective tissue which covers the skeletal muscles, the two layers 
being separated by great lymph spaces except in the septa where 
they become continuous. 
Sketch a cross-section of the skin, selecting for this purpose a 
