Unstriped Muscles.

The simplest of the muscular acquirements of mammals is of course that great mass of little structures which constitutes the unstriped musculature. I must admit that here again I am engaged with what the professed biologist may call trifles, but these, like some others of a corresponding rank, have a provoking quality of persistence, and display, if one may personify them, an insistent desire to know whence they come and why they are here. Some of these, like the one before us, may be comprehended in the great chapter of the Evolution of the Indifferent of which they form a page. This world, at any rate in the moral sphere, would be an intolerable house of bondage if there were not many things that matter not as well as things that matter, and there is reason to believe that in the process of the making of man and a vast number of forms below him there is a large field of structures, parts and organs, where things that matter not are to be found. One strange province of this realm is the coloura­tion of animals in certain regions where no eye ever can see the colour or can take any heed of the markings, treated very fully many years ago by Mr. Beddard in Animal Coloura­tion.

Unstriped muscle arises, as the striped variety does, from the mesoblastic muscle-plate and appears in nearly all organs, blood-vessels and skin, and as trade is said to follow the flag, so a development of new unstriped muscles must speedily be found in every new structure of the regions where unstriped muscle is found. The skin is the simplest, and less complicated by the presence of other structures than vessels and organs, where it also exists, but where it trespasses too much on the territory of selection for my immediate purpose. A small band of this muscle called an arrector, or erector, pili is attached to most, if not all, of the third of a million hairs which cover the skin of man, and is inserted into that side of each hair which forms an obtuse angle with the plane of the skin. This tiny structure is endowed with the quality of contracting in response to certain stimuli falling on the skin, so that it causes the hair to which it is attached to stand erect instead of sloping, and incidentally squeezes some of the secretion out of the sebaceous gland which lies in each angle. The human skin thus possesses about a third of a million minute muscular bands and shows no sign of parting with this old gift from a lower hairy stock, and whatever value, if any, their function be to their possessor they show a remarkable readiness to perform it efficiently. It makes their existence and persistence no clearer to call them vestigial, for one only thus throws the question of their origin much farther back. Undoubtedly they come from afar and were in full development in the earliest hair-clad mammals, so an ancestry reaching back to Monotremes or Marsupials is not to be lightly set aside. The raw material was undoubtedly formed in response to stimuli conveyed to the brain, and the earliest appearance of muscles which erected the hairs must have been wholly insignificant either upon the survival or comfort of the possessors.

A Remarkable Example.

The arrectores pili exhibit very little evidence of control or interference from the action of the brain, but there is one region of one animal, like the Rosetta stone that set Champollion at work, where a very simple hieroglyph is recorded. I have been able to find no other in all the hairy mammals I have examined than that startling pattern which the back of the lion, shown in Fig. [37], sometimes displays. That well-formed patch of reversed hair of roughly triangular shape which is frequently found on the back of a lion has been described and, as I interpret this strange structure, it would seem clear that neural change in some examples of this species has led to so persistent contrac­tion of the arrectores pilorum over a certain area of skin, and that these have permanently reversed the normal and primitive slope of the hair. I have never found it present in a lioness, and not in all cases of male lions. It marks its possessor with the brand of a fierce and especially savage character, and he is not able to screen it from the eye of the Zoologist as well as Milady did her brand of shame, until that fatal day when D’Artagnan disclosed it. This pattern on a lion’s back is strangely reminiscent of the ridge of bristling hair we see on the corresponding region of a fierce dog’s back when he is infuriated. In the latter it may be said to have selective value, as perhaps also is the bristling hair on the head of a gorilla when enraged, much in the same way as the Chinese warriors sought to alarm their enemies by terrifying grimaces, or those terrifying tones and expressions of face which the Tyrant man, really a coward, is said by such as Miss Wisk to exercise over the women of his circle. We may present all these to the Pan-Selectionist, but inasmuch as the short, bristling hairs on the back of a lion are on the one hand hidden by the mane from an animal in front, and on the other are so small as to be seen quite close if at all, the survival-value of the reversed pattern of hair in question is quite outside the province of selection. It is so manifestly under the control of cerebral action, that it may be compared, as an undesigned experiment, with that of man in placing harness upon a horse, as to the power of cerebral action in producing structure. Though, as far as I can learn, it stands alone, it is difficult to believe that such a thing as a unique example occurs in nature, but it is interesting and suggestive from the Lamarckian point of view, and even the opposing counsel must admit that it is among indifferent structures.

Facial Muscles of Expression.

This record in terms of hair of personal and ancestral emotions has, however, a link with certain more numerous and important striated muscles, such as the facial muscles of man and apes, modifications of the great platysma-sheet, and which are disposed in two layers, a deep and a superficial. This covers like a hood at the third month the head and neck of the embryo, and later assumes on the face its specialised form of certain bands which operate round the eyes and mouth. As they are of the striated kind these muscles can be moved at will, but their main action is much more under the government of the mental processes of their possessor. As they are fundamentally the same in apes and man very little new muscular structure arises in man, and little more than shaping or refining takes place.

The facial muscles which operate round the orbit have less mental action represented in them than those of the mouth, though the action of the special elevator of the upper eyelid is conspicuous among the expressions of a vigorous person. Both apes and man have muscles on each side which raise or lower the angles of the mouth, draw the angles upwards and outwards, and raise the upper and depress the lower lip; and, though the muscle of the mouth which corresponds to the orbicularis of the eye is not a continuous structure, but formed of interrupted bundles of fibres, it is powerful in closing the lips and active in the expressions. There are also in man scattered oblique fibres in the substance of the lower lip, well-developed and closely-set in a sucking child, and these in the adult are scattered and less conspicuous.

There is thus a remarkable set of structures in the face of a higher primate which convey mental emotion. As they also belong to animals with a high degree of convolu­tion of brain, though certain are found in lower mammals, their specialisa­tion is only to be accounted for by the long-continued involuntary expression of mental states existing in the particular form of primate. Professor Keith says in the work before referred to: “Muscles supplied by the facial nerve are the physical basis into which many mental states are reflected, and in which they are realised. Through them mental conditions are manifested. It is found that the differentia­tion of this sheet into well-marked and separate muscles proceeds pari passu with the development of the brain. The more highly convoluted the brain of any primate the more highly specialised are its facial muscles,”[74] and he points out in a smaller work[75] that in the gibbon, and monkeys of the Old and New Worlds the facial system becomes simpler and at the same time more robust, and he pictures the facial muscles as the “servants of the brain.”