Crural Herbst corpuscles in chicken and quail: numbers and structure

Herbst corpuscles were studied in the crural region of perinatal and adult chicken and quail in order to find out their number and dimensions and to learn more about their structure, especially in relation to size. Crural corpuscles are arrayed in an encapsulated string between tibia and fibula. They are closely packed together; a small number of corpuscles is found apart from the string, often attached to the periost. The strings of corpuscles are approximately 40 mm long in adult chicken and 20 mm long in the quail. The crural region of the chicken contains 382.8 +/- 90.9 (mean +/- SD) corpuscles, the numbers ranging from 301 to 582; in the quail, the mean number is 119.2 +/- 27.9, with a range from 83 to 167 corpuscles. In the chicken, one axon supplies an average of 1.60 corpuscles; in the quail, the relation of axons to corpuscles is approximately 0.92. In both species, final numbers of crural corpuscles are already attained before hatching and no difference is found in the mean number and range of corpuscles between perinatal and adult birds. In both chicken and quail, individual strings contain corpuscles of various sizes, from large to very small. The chicken corpuscles are generally twice as large in diameter and often longer than those of the quail. The corpuscles are composed of an axon terminal that projects two rows of axonal spines into the clefts of the inner core and ends with an ultraterminal bulb; the terminal is surrounded with a bilaterally symmetrical inner core, amorphous inner space containing collagen fibrils of various thickness, and a capsule. Large chicken corpuscles contain inner cores composed of up to 100 lamellae, while quail inner cores have half that number at the most. The capsules are usually composed of 8 to 10 lamellar layers in both species, but they are thicker in the chicken than in the quail. The possible functional significance of individual structural components of Herbst corpuscles is discussed.