This refers to breathing holes, spiracula, in the front plate, but there were also openings, sometimes of considerable size, in the backplate behind the vertical joint, through which the knight could hear and perhaps, by turning his head, see and speak to the squire who attended him. In the fifteenth century the demand for greater mobility and less weight in the armour that was used for actual battle had produced the Helmet or small helm, having a front which opened and a more or less flexible neck, the Bascinet, the Salade and other forms of head armour; and thenceforward the great helm was reserved for the uses of the tournament. [Illustration: FIG. 146.--Helmet. Fifteenth Century.] An example of helmet at Fig. 146, after Viollet-le-duc, will serve to explain its structure. The vizor, in two parts, opens upwards on a pivot, and the front opens sideways by means of a hinge to permit the helmet to be put on, and though there was a great variety in shape and construction they were all modifications of the methods of the example. The head was capable of movement, the laminated plates of the gorget giving a certain amount of flexibility from side to side as well as up and down, provision being also made for some amount of turning movement. As pieces of defensive mechanism helmets were very excellent, but were rarely associated with crests in the time of their actual use--though they were frequently so represented in the later times when heraldry had become out of touch with the armoured period and did not trouble to go farther back for its crest support than the most recent form of closed defence for the head. In all armour, and much besides helms is used in heraldry, it will be found useful to acquire a practical knowledge of its structure and method of working and also the practical reasons for the form of its various parts. By so doing it will become unnecessary to search for a model for every need, rather it will be possible in the case of a figure to draw the man and put the armour on him in the form that seems most suitable. Forms of greater or less simplicity can thus be designed as circumstances may dictate, as it may be desirable in the interests of light and shade to elaborate or minimize the details. Armour should be so designed that its principal lines help the composition and express the form in the most forcible, suitable and simple way. In an arm, for instance, which is of frequent occurrence as a crest, it should be observed how the gauntlet has its defence added to the glove, how its wrist fits over the arm piece, the arrangement of the elbow piece, the cubitiere, on its inner and outer sides with regard to the hollow of the arm, and so forth. By thus familiarizing oneself with the essential structure, it becomes possible to handle the subject with confidence in design, so that perspective, light and shade and the harmonious relationship of lines may be helped, while the structure appears convincingly right.