CHAPTER IX. 



THE INNERVATION OF GLANDULAR STRUCTURES. 



ALL the nerves which cause secretion of duct-bearing glands be- 

 long to the involuntary system, and their motor neurons, like 

 those to the involuntary muscles, all lie outside the central 

 nervous system. 



The duct-bearing glands may be divided into three sets ac- 

 cording to their origin : 



1 . Those derived from cells on the surface of the body, or 

 epidermal glands, such as the sweat glands. 



2. Those derived from cells in the surface of the gut, or endo- 

 dermal glands, such as the pancreas, liver, etc. 



3. Those derived from cells of the surface of the coelom, or 

 mesodermal glands, such as the kidney. 



It is generally stated that the epidermal glands are formed 

 by invagination of the surface epithelium, so that one would na- 

 turally suppose that their innervation could not differ from that 

 of the surrounding epithelial cells, which have not been in- 

 vaginated. These latter are not known to have any connexion 

 with efferent or motor nerve fibres but only with afferent or 

 sensory fibres, and it is inconceivable that the mere act of in- 

 vagination should alter the nerve supply. We should expect then 

 a priori that such glands would be innervated from fibres belong- 

 ing to the sensory rather than the motor part of the nervous 

 system ; yet the evidence is very strong that, both in the case of 

 the sweat glands and the prostate gland, secretion can be brought 

 about by the stimulation of anterior and not posterior spinal roots. 

 On the other hand it is possible that these cells, which are in- 

 vaginated, are not the same as the surrounding cells, but were 

 special glandular cells before invagination, which, though situated 

 in the epiblast, were connected with the motor side of the nervous 

 system, an innervation comparable to that of certain unstriped 

 muscle cells, which are also said to be derived from epiblast. In 



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