Innervation, Especially, Sensory Innervation of Mamma of Female Dog

Field: Veterinary (Health Sciences)

There is little essential difference, histologically speaking, between the nipple and the areola mammae of a female dog and those of man. Papillae are markedly formed into the epidermis and smooth muscle fibres in the corium are strongly developed in both cases. The difference consists in the absence of melanin pigment in the epidermis and the papillary layer of the canine mamma, the growth of groups of tufts in many spots on the root of the nipple down to the areola mammae in dog, and the absence of eccrine sweat glands and the strong development of apocrine glands in the canine mamma, not only in the areola butt also in the lower layer of the corium of the nipple and along the sinus lactiferi.Many vegetative nerve fibres are found distributed in the parenchym of the canine mammary glands, with their terminalreticulum (STÖHR) diffused circumferentially around the alveoli. No sensory nerve fibres, however, have been found in the mammary glands. The vegetative nerve fibres originating in the subcutaneous plexus in the nipple and the areola mammae end by forming their terminalreticulum in the areolar glands, the ductus and sinus lactiferi, the smooth muscle tissue and the papillary layer in the corium.The development of sensory fibres in the nipple and the areola mammae in dog is rather marked, much resembling those in human male (SUGA, 1949), and clearly indicates that these parts should belong to the skin of the external genitals.No intraepithelial fibres, MERKEL's touch cells and touch plates, which have been described by MARTYNOV (1925) as existing in the epidermis of the nipple and areola mammae, have been discovered in my canine specimens. Neither PACINIAN bodies were observed in my sections, but I presume that they do exist in an extremely small quantity.Small quantities of unbranched and very simple branched terminations are found in the papillary layer of the nipple and the areola mammae in female dog. Among the smooth muscle bundles in the reticular layer of the corium there are found comparatively many peculiar branched sensory terminations. These may be subdivided into the complex and the simple types. The medullated nerve fibres, after losing their myelin, throw out branches, which in most cases run peculiar, and in particular, zigzag courses, during which the size of the fibres undergo marked changes, before terminating. These special branched terminations are very similar to those found in human male nipple by SUGA and I take them to be peculiar to the nipple and areola mammae.As the only corpuscular terminations in the mammae of female dogs, I may mention the small number of genital nerve corpuscles I observed in the connective tissue of the surface layer of the stratum reticulare. These were incomparably poorer in development than those described by MARTYNOV (1925) as found in the nipples of other mammals and even inferior to the similar terminal bodies in human male nipples (SUGA, 1949). They belong to the type 2 of YAMADA's classification of genital nerve bodies (1951), while no corpuscle belonging either to his type 1 or type 3 was found in my canine specimens. This type 2 is represented by a capsulated terminal body, which contains extremely simple branched terminations of a few entering demyelinated nerve fibres, especially at the center of a syncytial inner bulb consisting of minute granular ground substance and special nuclei.The terminal territories of the sensory hair nerve fibres for the hair follicles found in the area extending from the nipple to the areola mammae are represented by simple hairneuro-shields (SETO). Consepuently, the development of the sensory hair nerve fibres is very poor, and their terminations are only formed of extremely simple indefinite terminations or simple plexus-like terminations, as in the follicle necks of the human downs.