The bodhrán is an old drum but a young musical instrument. Although it has existed in asia for centuries, it was introduced into traditional music performance only in the 1960s, and became common only in the 1970s.
I've heard differing opinions on the ultimate origin of the bodhán. Some writers believe that the drum originated in Africa and came to Ireland by way of Spain. Other people, including Henry Geraghty, believe that it originated in Central Asia, and was carried through Europe to Ireland by the Celtic migrations.

What is not in dispute, is that the drum languished for centuries outside the realm of musical performance. It was used in warfare and in various local celebrations, mostly as a noisemaker or primitive rhythm instrument. Until modern times, it was used by mummers and wren-boys in various local festivals. It apparently served double-duty as a husk sifter and grain tray.

Until the 1960s, it was uncommon outside southwestern Ireland; it was introduced to modern traditional music to Sean O Riada, who used it in his arrangements for Ceoltóirí Chualann and the Chieftains.

Construction

The crossbars were originally used to prevent the warping of the rim, which was made of wood that was bent green. Modern methods eliminate the structural purpose of the crossbars, and many drummakers now omit them. If you have a well-made drum, you should be able to remove the crossbars without any problem.
According to Ron Murphy, bodhráns were traditionally made with goatskin, sheepskin, and greyhound skin heads. He says that skins were prepared by burying them in lime for six to eight weeks, then soaking them in a river to wash away the hair. I have heard of modern drummakers using skins from donkeys, reindeer, calf, elk, deer, and buffalo. Most recently, I've heard that Fred Halpin is making tunable drums with heavy, tanned goatskin heads. Jesse Winch told me that this produces a drum with a very soft, mellow tone.

Perhaps the most significant functional development is the introduction of tunable bodhráns. Between six and twelve tuning screws move a ring which presses against the skin, allowing the drummer to tighten or loosen the skin to change the pitch and adjust for varying humidity. Johnny McDonagh told me that he conceived the idea and gave it to David Gormlie. Gormlie kept the first tunable drum he made, but gave the second to McDonagh, who still owns it.

I have seen three distinct types of tunable drums.

External tunables have the screws mounted outside the rim, with a metal ring circling the skin, much like a snare drum. This method prevents the drummer from playing the edge of the drum, but is usually much less expensive than other methods.

Internal tunables have tuning screws mounted inside the rim, with a tuning ring under the head, just inside the rim. The screws move the ring, which presses against the head, thereby increasing or reducing the tension of the head. Mance Grady has an interesting variation on this design; he has split the ring into separate segments, one for each tuning screw, so that he can adjust the tension of the head independently at each screw.

The newest variation on the tunable bodhrán is a patented design invented by Fred Halpin. His drums have tuning screws through rim itself. His rims are thicker than normal; as far as I could tell, the tuning ring is set into the upper edge of the rim.

Bodhran