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  Section: Anatomy of Vertebrate Animals » The Classification and Organization of the Mammalia
 
 
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The Proboscidea

 
     
 

These are massive animals, walking upon the extremities of the five toes, with which each foot is provided, and upon a great tegumentary cushion which unites these, and forms a flat sole behind them.

The nose is prolonged into a flexible proboscis, which is at once a strong, and a delicate, organ of prehension. The hairy covering is scanty in the recent species; but there were abundant long hair, and an undercoat of wool, in at least one extinct Proboscidean, the Mammoth (Elephas primigenius), which ranged over Northern Europe and Asia during the glacial epoch. The pinna of the ear is large and flat. The testes of the male remain in the abdomen, and the mammae of the female are placed between the fore-limbs.

The dorso-lumbar vertebrae amount to as many as twentythree, and not more than three of these are lumbar, so that the dorsal region is, proportionally, exceedingly long. There are four sacral vertebra, followed by a comparatively short tail. The centra of the vertebrae are far more flattened, from before backward, than those of any other terrestrial mammal, and this is particularly the case in the cervical region, whence it follows that the neck is extremely short.

The skull is enormous, even in proportion to the body, its size arising, in great measure, from the development of air cavities in the diploe. The interspace between the inner and the outer tables of the skull is often, in an old elephant, considerably greater than the diameter of the cerebral cavity itself. The cranial cavity is elongated and subcylindrical. The supraoccipital rises far upon the roof of the skull, so that the parietals are much narrower at the sagittal suture than elsewhere. The premaxillae are very large, and the nasal bones short, the nasal passages being nearly vertical. The jugal bone forms only the middle part of the jugal arcade. The rami of the mandible have a high perpendicular portion, and they are largely anchylosed at the symphysis, which is produced into a sort of spout.

The acromion of the scapula has a recurved process, such as is frequently found in the Rodents, to which order the Proboscidea present many curious approximations. There are no clavicles. In the antebrachium, the radius is permanently fixed (though not anchylosed) in the prone position, crossing the ulna obliquely. The carpal and metacarpal bones, and the phalanges, are remarkable for their short and thick form, and the manus is larger than the pes.
The skeleton of the African Elephant (Loxadon Africanus)
Fig. 108. - The skeleton of the African Elephant (Loxadon Africanus).

The ilia are immensely expanded transversely. The femur, which is not connected by any round ligament to the acetabulum, is relatively long and slender; and, when the animal is at rest, is directed perpendicularly to the axis of the trunk, not bent up, so as to form an acute angle with that axis, as it is in ordinary quadrupeds. The ham consequently occupies the middle of the length of the hind-leg; the flexion of which, at this point, when the animal walks, gives an elephant a gait which is strikingly different from that of other quadrupeds. The tibia is relatively short. The fibula is distinct and complete, and the bones of the pes have the same broad and short form as those of the manus. The hallux has only a single phalanx in some species.

The Proboscidea have only two kinds of teeth, incisors and molars, canines being entirely absent. The incisors are composed of dentine and cement, with or without a longitudinal belt of enamel, and, in the recent Elephants, are developed only in the upper jaw. As their growth continues for a long period, or throughout life, they usually take the form of long tusks, which project on each side of the upper jaw. The molar teeth are composed of dentine, enamel, and cement, and their crowns, when unworn, are always ridged, the ridges very often being made up of distinct tubercles. The intervals between the ridges are sometimes, as in the Asiatic Elephant, exceedingly deep, narrow, and completely filled up with cement; or, as in the African Elephant, they may be shallow and open, the cement forming only a thin coat. In the recent Elephants, only the two incisors are preceded by milk-teeth. The molars are, altogether, six on each side, above and below; they come into place and use successively, the hinder ones moving forward, in proportion as the anterior ones are worn down by the attrition of those which are opposed to them.

The stomach is simple and elongated, and there is a very wide caecum. The trilobed liver has no gall-bladder. The heart has two anterior cavae.

The cerebellum is left uncovered by the cerebral hemispheres; which, in the existing Elephants, are large, and have greatly-convoluted surfaces.

The male reproductive organs exhibit two very large vesiculae seminales, and four prostates. The uterus of the female has two cornua.

Some, if not all, species of the extinct genus Mastodon were provided with a pair of short tusks in the mandible, in addition to the large ones in the premaxillae. And in some of these animals, as in certain other extinct Elephants, the anterior grinding teeth had vertical successors. The Miocene genus, Dinotherium, possessed two large, downwardly-directed tusks, one on each side of the symphysis of the mandible, while there were none in the upper jaw. The second and the third anterior grinding teeth had vertical successors.

The Proboscidea are, at present, restricted to Asia and Africa, where they are represented by two very distinct forms to which the names of Loxodon (E. Africanus) and Euelephas (E. Indicus) proposed by the late Dr. Falconer may be very properly applied. The oldest rocks in which their remains occur are of Miocene age. Fossil remains of elephants occur not only in the Old World, but also in both North and South America.
 
     
 
 
     



     
 
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