. Zoology : for students and general readers . Zoology. THE PROBOSGIDIANS. 597 Period a fossil Sireuiau {HaUiheriuin) iuhubited the sliores of western Europe. In the structure of tlae sl;ull, their dentition and their her- bivorous habits the Sirenians in a degree connect tlie Ceta- ceans with the Ungulates. Order 7. Prohoscidia.—Only two representatives of this group are now in existence, the Asiatic and African elephant, a number of other forms having become extinct. The group is well circumscribed, when we consider the living species, but in the early (Eocene) Tertiary Period there existed
. Zoology : for students and general readers . Zoology. THE PROBOSGIDIANS. 597 Period a fossil Sireuiau {HaUiheriuin) iuhubited the sliores of western Europe. In the structure of tlae sl;ull, their dentition and their her- bivorous habits the Sirenians in a degree connect tlie Ceta- ceans with the Ungulates. Order 7. Prohoscidia.—Only two representatives of this group are now in existence, the Asiatic and African elephant, a number of other forms having become extinct. The group is well circumscribed, when we consider the living species, but in the early (Eocene) Tertiary Period there existed forms which indicate that the Proboscidians and Ungulates had a common origin. In the elephants the up- per incisors are enor- mously developed, while there are none in the lower jaw. There are no canine teeth, while the few molars are large,trans- versely ridged. In the elephants the ridges are numerous, the spaces between them filled with cement. The young mastodon has cement on the up- per surface of the tooth ; the ridges af- terwards become free and covered with enamel. A peculiari- ty in the elephant's skull is its large size, the brain cavity being very small in proportion to the bullc of the skull itself. To give lightness to what would be otherwise an insupportable weight, the cranial bones contain numerous large air-cells (Pig. 520). Another remarkable feature,from which the group takes its name, is the trunk or joroboscis, a long, thick, fleshy, flexible snout, growing from the front edge of the nasal. Fig. 519.—Skull of yotin^ elephant; 22, premax- illary bone containinj^ the root of the tusk, k ; 15, nagal bone ; 7, parietal bone or temporal region ; 26, molar, zygomatic arch ; e, lower jaw ; c, upper jaw ; m, molar tooth ; 21, maxilla ; 11, frontal; g, squamosal.—After Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not per
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectzoology, bookyear1879
