Passing to the north we see the central tower, possibly Norman as high as the roof, with a superstructure of later times. The pitch of the roof may have been altered in later times from a high pitch to a flat one, and the marks of the old roof may often be seen on the tower walls. Just below the eaves is the range of clerestory windows. Flying buttresses connecting the buttresses of the outer wall with those of the inner are frequent and produce a very graceful effect. Niches for statues are often carved upon the buttresses. Curious grotesquely-carved heads, called gargoyles, look down upon us from the gutters of the roof. The tracery of the windows is no indication of the age of the walls, as they have frequently been inserted in place of others of an older period. The porch is a large structure, and sometimes has a chamber, called a parvise, over it. The object of this chamber cannot always be determined. Sometimes it was the abode of the sacristan, and occasionally it was set apart for the use of an anchorite or recluse. The monastic buildings are usually on the south side in Benedictine monasteries, but sometimes on account of the nature of the ground they are on the north. On entering the church we view the nave, which is usually in three storeys--the main arcade, the triforium, which opens into a gallery or passage, and the clerestory. Sometimes the choir occupies two bays of the nave, but usually begins with the screen placed on the east side of the central tower. This screen was formerly the rood-screen, and a large crucifix stood on it; but at the Reformation all roods were destroyed, and sometimes the organ stands in its place. Entering the choir we see before us the high altar with a fine reredos behind it, so called from the French _L'arrière-dos_, meaning "embroidered hangings." On the south of this is the piscina, consisting of a hollow basin with a stone-drain, wherein the priest cleansed the sacred vessels after using them in the Holy Eucharist. On the same side are the sedilia, or stone seats for the clergy, frequently with richly-carved canopies. Then there are the beautifully-carved stalls with fine tabernacle work, and the _sub-sellæ_ or misereres (French, _miséricorde_) with their quaint carvings. It is a popular error, gravely perpetrated by some cathedral vergers and others, to suppose these misereres were a kind of ingenious trap for sleepy monks, who, when the heavy seat fell down with a loud bang, were detected in slumber and forced to do penance. They were so placed as a concession to human weakness in order that the monks or canons might lean against them during the long mediæval services, when sitting was not allowed. The eastern portion of the choir is called the presbytery.