1Cross, Tom Peete, and Clark Harris Slover. Ancient Irish Tales. New York: Barnes & Noble, 1936. 514-17. Original from Book of Ballymote (Leabhar Bhaile an Mhóta) c. 1391 Royal Irish Academy MS 23 P 12 fol., 7, p,b, col. b.
This tale may be read in its entirety here. The synopsis of this story is: Eochaid, the King of Leinster, escaped from Niall of the Nine Hostages at Tara, where he was being held prisoner. Eochaid fled toward his home country, pursued by Niall. He tried to find refuge in the home of Laidgrinn, a poet. He was refused sanctuary and in revenge burned the man's house. Niall caught up with him and brought him to his camp at Ath Fadat (Tullow) where he was fastened to the Holed Stone, and subsequently escaped by killing the nine men Niall had sent to execute him.

2Ryan, John. The History and Antiquities of the County of Carlow. Dublin: Richard Moore Tims, 1833. 19. This book may be read in its entirety here.

3O'Donovan, John, and Michael O'Flanagan. Letters Containing Information Relative to the Antiquities of the Counties of Carlow and Monaghan, Collected during the Progress of the Ordnance Survey in 1839. Vol. 2. Bray, 1927. 122-23.
From a letter from Eugene Curry, 8th August, 1839: "...while some labourers were turning up the soil...directly between the above perforated rock and the Ath Fada or Lorgforde on the Slaney, they met with a great number of skeletons at from two to three feet below the surface, and among other things, they met with several curiously formed graves containing urns with burned and unburned bones."

4Ryan, John. The History and Antiquities of the County of Carlow. Dublin: Richard Moore Tims, 1833. 338. This account may be read in its entirety here.
Rickets is a disease, now primarily suffered by children in developing countries, caused by a lack of vitamin D, calcium, or phosphate, or other dietary needs. It leads to softening and weakening of the bones.
William Wakeman's discussion (1903) of the Aghade Holed Stone and similar specimens may be read in its entirety here.

5Harbison, Peter. Guide to National and Historic Monuments of Ireland: including a Selection of Other Monuments Not in State Care. Dublin: Gill and Macmillan, 1992. 49.

6Jackson, Kenneth Hurstone. The Oldest Irish Tradition: A Window on the Iron Age. Cambridge: Cambridge University Press, 1964. 44, note 1.
This entire note may be worth repeating: "I should emphasize that what I mean here is the historiasity of persons and events; for instance, Conn and Eoghan, kings of the north and south of Ireland respectively, reputed by the sages to have lived in the second century, are quite obviously legendary and indeed mythological characters, and the events in which they are said to have taken part are clearly bogus. The same is true of still later characters like Cormac mac Airt. It is probably not too much to say that the earliest figure whom we can regard with any confidence as at all historical is Niall of the Nine Hostages. Equally, then, the characters Conchobar and Cu Chulainn, Ailill and Medb and the rest, and the events of the Cattle Raid of Cooley, are themselves entirely legend and purely un-historical. But this does not mean that the traditional background, the setting, in which the Ulster cycle was built up is bogus; the whole of this lecture is intended to show that it is not."

7MacCana, Proinsias. Celtic Mythology. London: Hamlyn, 1970. 120.
When Niall asked the crone, " 'And who art thou?' 'Royal Rule am I' she answered." (Ní Bhrolcháin, Muireann. "Women in Early Irish Myths and Sagas." The Crane Bag: "Images of the Irish Woman" 4.1 (1980): 12.)
In the story, Niall's descendants will rule unbroken, except for two kings who would descend from Fiachra, the result of his giving the crone a brief kiss of his own.

8"Niall of the Nine Hostages." Wikipedia. Wikimedia Foundation, 06 Nov. 2012. Web. 11 June 2012. <http://en.wikipedia.org/wiki/Niall_of_the_Nine_Hostages>.
According to this entry, "The sources for the details of Niall's life are genealogies of historical kings, the "Roll of Kings" section of the Lebor Gabála Érenn, Irish annals such as the Annals of the Four Masters, chronicles such as Geoffrey Keating's Foras Feasa ar Éirinn, and legendary tales like "The Adventure of the Sons of Eochaid Mugmedon" and "The Death of Niall of the Nine Hostages". These sources date from long after Niall's time and their value as history is limited at best...the traditional roll of kings and its chronology is now recognised as artificial. The High Kingship did not become a reality until the ninth century, and Niall's legendary status has been inflated in line with the political importance of the dynasty he founded."

9Keating, Geoffrey, John O'Mahony, and Michael Doheny. Foras Feasa Ar Eirinn Do Réir an Athar Seathrun Céiting, Ollamh Ré Diadhachta. The History of Ireland, from the Earliest Period to the English Invasion. New York: P.M. Haverty, 1857. 390.
This account may be read in its entirety here.

10"Niall of the Nine Hostages." The Larkin Clan. Web. 12 June 2012. <http://www.larkinclan.eu/niall.htm>.

11"Medieval Irish Warlord Boasts Three Million Descendants." The New Scientist. Web. 12 June 2012. <http://www.newscientist.com/article/dn8600-medieval-irish-warlord-boasts-three-million-descendants.html>.
From the story: "The study says the chromosome has also been found in 16.7% of men in western and central Scotland and has turned up in multiple North American population samples, including in 2% of European-American New Yorkers...Though medieval Ireland was Christian, divorce was allowed, people married earlier and concubinage was practised. Illegitimate sons were claimed and their rights protected by law...As in other polygamous societies, the siring of offspring was related to power and prestige...one of the O'Neill dynasty chieftains who died in 1423 had 18 sons with 10 different women and counted 59 grandsons in the male line."
Another scientist, Ugo Perego, a senior DNA researcher at Sorenson Molecular Genealogy Foundation, determined that Mormon prophet Joseph Smith Jr. was definitely descended from Niall (http://www.genealogyblog.com/?p=8663).

12Grinsell, L.V. "Some Aspects of the Folklore of Prehistoric Monuments." Folk-lore 48 (1937): 252-53.
An author in 1912 suggested that passing an infant through the aperture in an ancient stone, "...may be an echo of a rite of symbolic rebirth." (Ffrench, J. F. M. Prehistoric Faith and Worship: Glimpses of Ancient Irish Life.. London: D. Nutt, 1912. 25-6.)

13Weir, Anthony. "Potency and Sin: Ireland and the Phallic Continuum." Archaeology Ireland 4.2 (1990): 54-55.
In 1895 Wood-Martin wrote, ""The original purpose for which the large apertures were utilized seems to have been a literal as well as a symbolic means whereby an ailment, disease, or sin might be left behind, or got rid of, also as a symbol by which a compact could be ratified, or an oath taken, by a well-known and public act. The postulants, at first, probably crawled through the orifice; then when it, through change in custom, became diminished in size, they probably passed a hand, or, if a compact was to be made, clasped hands through it. The act of a bride passing her finger through her wedding ring may be but a survival of the ceremony when the woman would have had to crawl through an aperture in a sacred stone..." (Wood-Martin, W. G. Pagan Ireland an Archæological Sketch; a Handbook of Irish Pre-Christian Antiquities. London: Longmans, Green, 1895. 308.)

14"Niall of the Nine Hostages." Wikipedia. The sources disagree as to the which countries supplied each of the nine hostages.