Depth, I, H, of the neck in its narrowest part (a half-head), 0·30 metre. It is frequently greater; this is noticeable in all instances where the superior parts of the neck are deficient in fineness. It is this which we see in draught horses, and in those which become too fleshy (G. and B.). Distance, O, R, of the internal commissure of the eye from the superior border of the commissure of the nostril (G. and B.) (a half-head), 0·30 metre. It is more considerable on the common head, and on that which is too long. Distance, A, O, from the nape to the internal angle of the eye, 0·22 metre. This distance is equivalent to the thickness of the head, P, Q, taken perpendicularly from the profile of the anterior surface, and passing at the level of the maxillary fissure and spine. It is, again, equal to Q, O, from the internal angle of the eye to the maxillary fissure; and to P, G, from the middle of the face to the commissure of the lips (G. and B.). The distance, P, E, from the middle of the face to the maxillary spine is about the sixth of the total length of the head--0·10 metre. [Illustration: FIG. 108.--PROPORTIONS OF THE HEAD OF THE HORSE, VIEWED IN PROFILE (AFTER COLONEL DUHOUSSET).] The line B, E, reckoned from the extremity of the lips to the maxillary spine, is equal: To E, F, from the maxillary spine to the external auditory meatus, to be seen only on the skull; To H, G, from the insertion of the neck in the trough to the commissure of the lips (G. and B.); To Q, R, from the maxillary fissure to the superior commissure of the nostril (G. and B.); To Q, B, from the fissure of the maxilla to the border of the lips (G. and B.); To O, D, from the internal angle of the eye to the angle of the lower jaw, provided that the line C, D be in proportion (G. and B.). [Illustration: FIG. 109.--THE SAME DESIGN AS THAT OF FIG. 108, ON WHICH WE HAVE INDICATED, BY SIMILAR LINES, THE PRINCIPAL CORRESPONDING MEASUREMENTS. Half the length of the head, and the dimensions which equal it; distance which separate the nape from the internal angle of the eye, and the dimensions which equal it; distance which separates the internal angle of the eye from the border of the lips, and the dimensions which equal it.[64]] [64] It is thus that in our teaching, but by means of lines of different colours, we present the proportions reproduced in Fig. 108. Experience has demonstrated to us that this replacement of letters by conventional lines renders the proportions more easily appreciable, and that these lines, striking the eye more forcibly, then impress themselves better on the memory. Fig. 111 bears the same relation to Fig. 110. Finally, very frequently to O, H, from the internal angle of the eye to the insertion of the throat into the maxillary trough (G. and B.). An equality still more frequent is that which exists between the distances: O, B, from the internal angle of the eye to the margin of the lips;