22 ANATOMY OF THE RABBIT. 
the general surface of the body the hair follicles are arranged in 
groups (Fig. 5), and on the lips certain large follicles are set apart 
for the production of the greatly enlarged sensory hairs or vibrissae. 
Connected with the hair follicles are thin strands of smooth muscle, 
the arrectores pilorum (Fig. 2, a,a’). They are placed in the 
broad angles formed by the inclined follicles with the corium and 
their contraction throws the hair into a more nearly erect position. 
Epithelial glands are ingrowths 
of the general layer, the cells of which 
become greatly modified as secreting 
structures. The lumen or cavity 
of the gland, in most cases greatly 
complicated through the division of 
the gland substance, is connected 
with the general surface by a duct 
which serves to carry away its 
secretion. In some cases the con- 
nection of a gland with the epithelial 
surface is embryonic, and in the 
adult condition the gland is found 
separated from the epithelium from 
which it was originally formed. This 
condition is represented by the 
thyreoid and thymus glands of the 
neck and thorax respectively. In 
other cases the secreting element is 

EG esha, 
Diagram of a multi- 
cellular gland: al., alveolar type; d., 
duct; ep., general epithelium; t., 
tubular type. B, The pancreatic duct 
and associated portion of the duo- 
denum in the rabbit. 
a single cell, the latter thus repre- 
senting a unicellular gland lying 
directly in the general layer. The 
mucus-secreting goblet cells of the 
intestinal wall are structures of this nature. Typical epithelial 
glands are accordingly external secreting glands in the sense that 
the secretion is discharged and utilized on a free surface. There 
are many structures, such as the suprarenal and pituitary bodies, 
commonly described as internal secreting glands, the products of 
which as hormones or chemical bodies of various kinds have a 
modifying effect upon functions in outlying parts of the body. 
They are not of necessity epithelial in origin and their resemblance 
to ordinary glands is usually only a matter of superficial appearance. 
