Another figure on the north side of the north-west turret, for some time assumed to be St. Christopher, is now assigned to St. Birinus, or possibly with more truth to St. Nicholas, who had an altar dedicated to him, "probably just at the back of this spot." On the apex of the west front is an ancient carving of a bird on a scroll, which has puzzled many specialists. Mr. Armfield believes it to be intended for a dove, the emblem of the Holy Spirit, in a scroll to typify The Word, and thus with the "Majesty" near, to be a representation of the three persons of the Trinity, in a mode in accordance with English taste. =The North Porch= is a massive structure of two stories. The upper, now used as the dean's muniment room, has, like a similar example at Christchurch, Hants, no certain indication of its original use. Whether it was a dwelling for sacristans, a school, or a library, was doubtful; but later opinion thinks it was unquestionably used by the sacristans, since it is said that "the sub-treasurer of Sarum, who was usually one of the vicars choral, pledged himself to see that the clerks told off for given duties slept in the church in their accustomed places; and for himself he promised that unless lawfully excused, he would sleep each night in the treasury." Against this theory, however, it might be urged that the muniment room at the angle of the south-east transept is identified as the ancient treasury. This porch, sometimes called the Galilee, was possibly a place where penitents met, and from which they were expelled from the church on Ash-Wednesday until Maundy Thursday. Externally, although of exquisite proportions, it has no very important details, yet its pinnacles deserve notice; but the interior is very beautiful, the walls have sunk panelling, a base arcade of foliated arches, and in the upper tier large foliated circles with sub-arches, each comprising two trefoiled arches with quatrefoil heads. Mr. G.E. Street, who thoroughly appreciated this particular period of English Gothic as his work at the New Law Courts proves, just before his death restored this part of the cathedral admirably. Another porch, formerly the entrance to the north transept, removed by Wyatt for the most trivial reason, is now in the grounds of the college which occupies the site of the secular buildings belonging to the church of St. Edmund, founded in 1268. =The Exterior= of the =Nave= is simple, but with excellently disposed features. The triple lancets of the clerestory occur in pairs between flying buttresses with tall finials; below these, in the aisles, are two two-light windows, divided by lesser buttresses terminating in gables.