"The bulge" as portrayed through photomicrographs


View Figure  		Fig. 11  "The bulge" is not a bulge, but bulges. Bulges serve as sites of attachment for fascicles of smooth muscle (hair erector muscle), as is evident in this photomicrograph.

View Figure  		Fig. 12  Bulges of a follicle in vertical section. Bulges are knobby epithelial protuberances from the lower half of the isthmus and, in a random section such as this one, may be bare of any muscles of hair erection. Step sections, however, would show attachments of those muscles to bulges.

View Figure  		Fig. 13  Bulges of a follicle cut at a tangent. A follicular bulb partially envelops a follicular papilla and above that unit bulges from the isthmus appear to arborize.

View Figure  		Fig. 14  Bulges of a follicle cut in cross section. Fascicles of muscle of hair erection are apparent in the lower part of this photomicrograph, but in this section none is seen to attach to bulges. In vivo, however, each bulge is wedded to a muscle of hair erection.

View Figure  		Fig. 15  Germ-like structure continuous with the base of the isthmus of a follicle in early anagen. The germ and papilla of this follicle in early anagen are situated at some distance from bulges of the isthmus above it. Muscles of hair erection shown at the lower right of the photomicrograph point in the direction of the bulges. We infer that a follicle at the outset of anagen derives from germinative cells at the base of the isthmus and that bulges are irrelevant to the follicular cycle, serving only as sites of attachment for muscles of hair erection.

View Figure  		Fig. 16  Trichofolliculoma. This stereotypical follicular hamartoma is characterized by absence of muscles of hair erection and of bulges. Despite lack of bulges, each of the innumerable aberrant follicles that constitute a trichofolliculoma undergoes a cycle, as evidenced by the presence of countless hair shafts among corneocytes in the infundibulo-cystic component of the hamartoma, some of which are pictured here.

View Figure  		Fig. 17  Induction of a follicle from infundibular epithelium. A folliculo-sebaceous unit on the left of this photomicrograph is continuous with the mid portion of an infundibulum of a follicle on the right. In short, a folliculo-sebaceous unit may be induced from germinative cells of an infundibulum; bulges are not requisite for induction of follicles.

View Figure  		Fig. 18  Induction of a follicle from epithelium of an infundibular cyst. The lower part of a follicle, in miniature, is continuous with infundibular epithelium that lines a cyst. The phenomenon demonstrates that induction of a follicle may occur without a "bulge."

View Figure  		Fig. 19  Mantles and bulges. The bowed epithelium that protrudes from the junction of infundibulum and isthmus of two neighboring vellus follicles represents mantles, i.e., anlagen and residua of sebaceous glands and ducts. The curved cords of epithelium that emanate from the isthmus of both follicles are bulges that play no part in either formation of sebaceous units or in initiation of anagen. At the outset of anagen, germinative cells at the base of the isthmus are directed by a follicular papilla to give rise to a germ-like structure like the one at the base of the follicle at the extreme left. Note in that follicle the distance between bulges and the unit of germ and papilla as it appears at the start of anagen. A rare finding (we have seen it only in the section illustrated in this photomicrograph) is origin of an inferior segment of a follicle in early anagen from a bulge (pictured in the follicle in the middle).

View Figure  		Fig. 20  Hair follicles and muscles of hair erection in a 19-day old SENCAR mouse. Four muscles of hair erection can be seen in this photomicrograph and three of them are connected to follicles. At none of the sites of attachment, however, is there a hint of a bulge. The gentle curve of the isthmus of the follicle on the far left is not to be mistaken for knobby protuberances known as bulges. Follicles in a mouse, unlike those in a man, display neither a bulge nor bulges.