Page:EB1911 - Volume 22.djvu/419

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405
PROBOSCIDEA

restrained, his self-respect is carefully developed; the family benefits, the home is not broken up, the wages still come in, and if the prisoner is a mother and a wife, it is, of course, most important that she should retain her place in the home; the prisoner does not “lose his job ” nor his mechanical skill if he is a skilled Workman. Lastly, the system is far cheaper than imprisonment. The prisoner keeps himself and his family, and one officer can attend to from 60 to 80 prisoners.

In the United Kingdom the probation system has been applied to young offenders by the Prevention of Crime Act 1908. That act empowered the prison commissioners to place offenders on licence from the Borstal Institution (see JUVENILE OFFENDERS) at any time after six months (in the case of a female, three months), if satisfied that there was a reasonable probability of their abstaining from crime and leading a useful and industrious life. The condition of their release is that they be placed under the supervision orjauthority of some society or person (named in the licence) 'willing to take charge of the case. This is, of course, only a limited application of the system of probation, for those detained in a Borstal Institution are offenders between the ages of sixteen and twenty-one who have been convicted of an indictable offence. It does not apply to those of full age, nor to those under twenty-one years of age who have been committed to prison for minor offences. It has been long held by English prison reformers that young persons under the age of twenty-one should not be committed to prison, unless for serious offences, but that they should be put under some system of probation. Legislation to this effect was foreshadowed by the home secretary in his speech on prison reform in the House of Commons on the zoth of July 1910.


PROBOSCIDEA (animals “ with a proboscis ”), the scientific name of the group of mammals represented at the present day only by the two species of elephant. Although here regarded as a sub-order of UNGULATA (q.-v.), the group is sometimes accorded the rank of an order by itself.1 The existing elephants are widely sundered from all other living mammals, and for a long time palaeontology afforded but little clue as to their ancestry. Discoveries made during the first few years of the zoth century in the Lower Tertiary deposits of the Fayum district of Egypt have, however, brought to light the existence of several kinds of primitive proboscideans which serve to link the group with other ungulates, and likewise apparently indicate affinity with the Sirenia.

The following are some of the leading characteristics of existing elephants. The combined upper lips and nose are produced into a long muscular, flexible and prehensile proboscis, or trunk, with the nostrils at its tip. The teeth consist of a pair of large upper permanently growing incisors ortusks; and a set of cheek teeth having their crowns composed of a series of tall transverse vertical plates gradually increasing in number from the first to the last of the series; and only portions of two of these teeth being in use at any one time. There are no clavicles; and the limbs are stout, with their component segments placed nearly in a vertical line, and the upper segment, especially in the hindlimb, the longest; the radius and ulna are distinct, the latter articulating extensively with the carpus; the fibula and tibia also distinct; the astragalus very fiat on both surfaces; and both front and hind feet short, broad and massive, with 'five toes (though the outer pair may be more or less rudimentary), all encased in a common integument, though with distinct, broad, short hoofs; third digit the largest. Two anterior venae cavae entering the right auricle. Stomach simple. A capacious caecum. Testes permanently abdominal. Uterus bicornuate. Placenta deciduate and zonary. Teats two, pectoral.

In order to understand the peculiar nature of the dentition, it is necessary to discuss to some extent those of the immediate ancestors D ua of the true elephants, such as the mastodons (see °" °"' MASTODON). As regards the mcxsors, or tusks, which 1 Cuvier's order Pachydermata (Gr. -mxffs, thick and 5ép;.¢a, skin), containing the elephants, hippopotami, rhinoceros, swine, tapirs, hyraxes, &c., is now abandoned, its members now forming the orders Proboscidea and Hyracoidea and the sub-order Parissodactyla.

A few Artiodactyla are also included.

project largely out of the mouth, and are of an elongated conic al form and generally curved, these are composed mainly of solid dentine, the fine elastic quality and large mass of which renders it invaluable as “ ivory ” for commerce and the arts. A peculiarity of the dentine of t he Proboscidea is that it shows, in transverse fractures or sections, fine lines proceeding in the arc of a circle from the centre


FIG. I.-Longitudinal Sections of the Crowns of Molar Teeth of various Proboscideans, showing stages in the gradual modification from the simple to the complex form. The dentine is indicated by transverse lines, the cement by a dotted surface, and the enamel is black.

I, Mastodon americanus; III, Elephas africanus; ll, Elephas (Stegodon) insignis; IV, Elephas primigenius. to the circumference in opposite directions, and forming by their decussation curvilinear lozenges, as in the “ engine-turning" of the case of a watch. The enamel-covering in existing species is confined to the extreme apex, and very soon wears off, but in some extinct species it forms persistent longitudinal bands of limited breadth. The tusks have small milk-predecessors, shed at an early a e.

gAs regards the cheek-teeth, these are composed in the mastodons of a variable number of enamel-covered transverse ridges, often divided into inner and outer columns, which may partially alternate, and complicated by smaller additional columns; but in the unworn tooth they stand out freely on the surface of the crown, with deep valleys between (fig. I, I). In the elephants the ridges are increased in number, and consequently become narrower from before backwards, while they are greatly extended in vertical height. In order to give solidity to what would otherwise be a comb-like tooth, the whole structure is enveloped and united in a large mass of cement, which completely fills the valleys, and gives a general smooth appearance to the unworn tooth; but as the wear consequent upon the masticating process proceeds, the alternate layers of tissue of different hardness—cement, dentine and enamel-which are disclosed upon the surface form a line and efficient grinding instrument. The intermediate stages between the molar of a modern elephant and that of a mastodon are so fully known that it is not possible to draw a definite line between the two types of tooth structure (see fig. I, II, III, IV).

As regards the mode of succession, that of modern elephants is very peculiar. During the complete lifetime of the animal there are but six cheek-teeth, which it will be convenient to allude to as molars, on each side of each jaw, with occasionally a rudimentary one in front, completing the typical number of seven. The last three represent the molars of ordinaryfmammals, those in front are milk-molars, which are never replaced by permanent successors, the whole series gradually moving forwards in the jaw, and the teeth becoming worn away and their remnants cast out in front, while development of others proceeds behind. The individual- teeth are so large, and the processes of growth and destruction by wear take place so slowly, that not more than one, or portions of two, teeth are ever in place and in use on each side of each jaw at one time, and the whole series of changes coincides with the usual duration of the animal's life. On the other hand, the earlier representations of the proboscidean series referred to below have the whole of the cheek-teeth in place and use at one time, and the milk-molars vertically displaced by premolars in the ordinaxély fashion. Among mastodons transitional forms occur in the mo e of succession as well as in structure, many species showing a vertical displacement of one or more of the milk-molars, and the same has been observed