Abstract
In the cutaneous part of human adult lip, a small part of the sensory fibres run into the papillary layer of corium and end there in simple branched terminations, as was the case in the scalp, but the greater majority end in the special tissue in the hair follicle neck as the so-called sensory hair-nerve fibres.
The sensory hair-nerve fibres and their terminations are much better developed in the cutaneous part of the lip than in the scalp, abreast with the better development of the special tissue in the hair follicle neck in the former. Namely, the terminal area of the hair-nerve fibres in the scalp consists chiefly of SETO's one-sided neuro-shield, but in the cutaneous part of the lip it takes in most cases the form of hair-nerve tube completely surrounding the outer root sheath. The terminations of the sensory fibres ending in these terminal areas are mainly of more complex types. Simple undefinite-shaped terminations found often in the scalp are absent here, while the more complex terminations of the plexus-like, the serrate, and sometimes the intermediate of the two above types are found here, in far greater complexity than in the scalp.
It must be specially mentioned that in the zone approaching the transitional part on the lip, where the hairs are very ill-developed downs in spite of the strong development of the sebaceous glands, some plexus-like terminations of sensory fibres far stronger in development than the above mentioned complex terminations are found in the special tissue around the outer root sheath, from which sometimes fibres are sent out to form a secondary terminal plexus outside the hair outer root sheath further upward.
In our study, we failed to discover either the intraepithelial fibres in the outer root sheath reported by KADANOFF or the touch cells and the intraepithelial fibres ending in contact with them allegedly found by SZYMONOWITZ.
The vegetative innervation of the cutaneous part of the lip is similar to that in general hairy skin. The vegetative fibres always pass over into STOEHR's terminalreticulum, which in most cases stands in tactile control over the tissue cell.
