It will not escape the mind of any person who has followed critically this process of inquiry, that in Chapter VII, where the immense variety of the patterns found on the side of the horse’s neck are described, there is an apparent resemblance between them and those on the ventral or under surface of the neck. The former were shown to be due to natural forces, those of sustained and repeated underlying muscular traction of muscles and jolting of the neck in locomotion; whereas in this chapter a considerable number of patterns have been brought forward and pictured on the under surface, and these are attributed to artificial pressure from harness. The reasonable objection is raised, “Why should the former be considered natural and the latter artificial in their origin?”
The answer to this is supplied by a consideration of the muscles shown in the two contrasted regions. In Figs. [3], [4] and [5], the muscles of the side of the neck are shown to be remarkably strong and numerous (in three layers), and diverging in their directions. In the muscles of the under surface of the neck of the horse, see Fig. [12], the muscles of the two sides shown are nearly parallel and no conflict of opposing or diverging muscles can well take place in this “debateable land.” If there were much divergent or opposing action going on it would, of course, produce the effects on the hair towards the upper part of the neck, where the muscles tend to diverge more and more as they pass to the head, and I have stated above that not a single instance in many thousands of horses has been found above the level where a loose collar ceases to rub when jolted upwards. This is very conclusive on the matter of diverging or opposing muscular action.
Then again the jolting in locomotion, which, in the case of the side of the neck is probably more effectual in producing changes of hair than even muscular traction, is almost absent from the under surfaces, as can be learned from careful watching of the motion of a horse.
Another reason which meets this objection very fully is that I have shown that 300 cart horses presented 277 of their number with reversed areas of patterns in the middle line of the under surface of the neck and these thick-necked animals are just those in which the collar is closely applied to the front of the neck in their heavy draught work, thus rubbing almost incessantly against the lie of the hair. In the thinner necks of the hackneys there are comparatively few indeed of the patterns found here and their collars as a rule fit very loosely and badly, and these frequently show a jolting up and down clear of the neck, which is seldom if ever present in a well-formed cart horse.
Further proof of this is shown by the simple fact that it is under the collar and within its range of movement that the changes of hair are produced.
No artificial pressure such as that of a collar is exerted on the parts of the side of the neck where the patterns are found; so I would submit that these two selected and much-disturbed areas owe their hair-patterns to two wholly different forms of mechanical cause.
I referred in the Preface to an important criticism of my earlier book on The Direction of Hair in Animals and Man, and will now treat this in some degree of detail. It is from the pen of an eminent American biologist, then Miss Inez L. Whipple,[59] now Mrs. Wilder Harris, and it is a careful, independent and thoughtful contribution from one who by her studies in this field and in the study of the mammalian palm and sole is widely known, and as widely respected.
Miss Whipple refers on page 403 to certain whorls and featherings on the backs of the lion, ox, giraffe and larger antelopes, which I then attributed to the action of the panniculus carnosus in shaking off flies. I am free to confess that the action then invoked by me was inadequate and incorrect and the explanations now given of them in Chapters X. and XI. on the ox and the lion, I think, are less open to criticism.
Again on page 404 she mentions the view formerly expressed as to the cause of the reversal of hair on the chest of man. This, also, I have reconsidered fully in Chapter XIII. where the action of the platysma muscle is held to be the cause of that remarkable reversal.
On page 403 the mistake I made in calling the reversed area over the ischial tuberosity of the ischium in a dog a whorl is pointed out. This is corrected in Chapter VI. on the Dogs.