176 Wort man — Studies of Eocene Mammalia. 



placed and is much rounded; the tuber of the calcaneum is 

 short and incurved ; the cuboid is high, broad from side to 

 side, and of comparatively little dorso-palmar thickness ; there 

 are never less than "five digits, and with the exception of the 

 marmosets and man, the hallux is always opposable ; the meta- 

 tarsals are slightly interlocking, and their distal extremities, 

 exclusive of the hallux, display a characteristic pattern, com- 

 pressed from side to side, much rounded from before back- 

 ward, and with progressive disappearance of keels, grooves, 

 and sesamoids of the flexor tendons ; the phalanges are 

 elongate and curved, and the unguals are in various stages of 

 transition from claw to nail ; the distal extremity of the meta- 

 tarsal of the hallux is always provided with sesamoids, and has 

 a distinct keel and grooves ; its opposability is shown by its 

 deeply excavated proximal extremity and the convex surface 

 of the internal cuneiform, and its terminal phalanx is always 

 flattened and nail-like. 



The Mantis. — The manus has the power of complete prona- 

 tion and supination ; the carpus is relatively high and narrow, 

 and its proximal articular surface is much arched from side to 

 side ; the unciform and magnum have great relative height, 

 and a centrale may or may not be present; the metacarpals 

 have characteristic globular extremities, in which the keels, 

 grooves, and sesamoids are little developed, and disappear com- 

 pletely in the higher forms ; the phalanges are elongate, and 

 the unguals may be compressed and clawlike or depressed and 

 nail-like ; the pollex is very generally present and, with the 

 exception of the marmosets and some lemurs, is always oppos- 

 able and nail-bearing ; its opposability, like that of the hallux, 

 is indicated by the character of its articulation with the 

 trapezium. 



The chief characters of the other parts of the skeleton are 

 the following : The teeth have brachyodont crowns with low 

 rounded cusps ; the incisors are very generally reduced to two 

 above and below, but exceptionally may be two above and one 

 below (Tarsius), or, again, one above and below, with rodent- 

 like modification {Mixodectes, Microsyops, Metacheiromys, 

 and Cheiromys) ; the premolars rarely become molariform, but 

 progressively decrease in number to two above and below; the 

 orbit, except possibly in a few instances, is always encircled by 

 bone posteriorly, the orbital and temporal fossae are separated 

 by a bony partition in the higher forms, and the eyes are 

 directed forward ; the mandibular rami are early coossified in 

 the more advanced species ; the limbs are elongate and well 

 developed, and clavicles are always present ; the coracoid is 

 large, the olecranon is short, and the fibula is very generally 

 unreduced ; the astragalus is without an astragalar foramen. 



[To be continued.] 



