PROBOSCIDEA. 583 



owing to the length of the humerus and yet more of the 

 femur elbow and knee are lower than usual ; the carpal and 

 tarsal bones have flat surfaces ; the feet are broad and bear 

 five hoofed toes embedded in a common integument. There 

 are no clavicles. 



The skull is very large, being adapted to support the 

 proboscis and tusks, and to afford a broad insertion for the 

 large muscles. In most of the bones there is during growth 

 an extraordinary development of air-spaces, which com- 

 municate with the nasal passages. The nasal bones are very 

 short ; the zygomatic arch (formed anteriorly by the maxilla, 

 medianly by the small jugal) is slender and straight. The 

 neck is very short. 



The dentition is unique. The two upper incisors or tusks 

 are mainly composed of solid ivory; the enamel is restricted 

 to the apex and soon wears off. As the tusks grow, their 

 roots sink through the premaxillse into the maxillae. There 

 are no canines nor premolars. The molars are very large, 

 and the enamel is very much plaited, forming a series of 

 transverse ridges enclosing the dentine, and united to one 

 another by cement. Thus on the worn tooth there are 

 numerous successive layers of enamel, dentine and cement. 

 Extinct forms show transitions between this complex type 

 and that of a horse. In a lifetime there may be six molar 

 teeth on each side of each jaw ; the anterior three seem to 

 be persistent " milk-molars," the last three are true molars, 

 but of these only one or portions of two can find space at 

 a time. The series gradually moves forward as the front 

 parts are worn away and cast out. 



The brain is highly developed. 



The stomach is simple, and there is a large caecum. 



There are two superior venae cavas entering the right 

 auricle. 



The testes remain abdominal in position. 



There are two pectoral mammse; the uterus is bicornuate.: 

 the placenta is non-deciduate and zonary. 



Elephas, Jf|, now represented by the Indian Elephant (&'. indicus) 

 (with parallel folds of enamel on the molars and ears of moderate size) 

 and the African Elephant (E. africanus) (with lozenge-shaped folds of 

 enamel and very large ears). 



The mammoth (A", frimigenius) belonged to the Pleistocene period, 

 and had a wide geographical range, occurring for instance in Britain. 



