XII. 



PHYLUM CHORDATA 



499 



The tibia has at its proximal end two articular surfaces for 

 the condyles of the femur ; distally it has also two articular 

 surfaces, one (internal) for the astragalus, the other for the 

 calcaneum. The fibula is a slender bone which becomes 

 completely fused distally with the 

 tibia. 



The tarsus (Fig. 281) consists of 

 six bones of irregular shape ar- 

 ranged in two rows, one of the 

 bones the navicular (nav.) being 

 intercalated between the two rows. 

 In the proximal row are two bones 

 the astragalus (ast.) and the cal- 

 caneum (cat.) both articulating with 

 the tibia; the calcaneum presents 

 behind a long calcaneal process. The 

 distal row contains three bones, the 

 mesocuneiform, ectocuneiform and 

 cuboid (cub?) ; the ento-cuneiform, 

 which commonly forms the most 

 internal member of this row in other 

 Mammals, is not present as a 

 separate bone. 



There are four metatarsals, the 

 hallux or first digit being absent. 

 Each of the digits has three pha- 

 langes, which are similar in character 

 to those of the manus. 



ir j 



FIG. 281. Lepus cuniculus 

 Skeleton of pes ; ast. astra- 

 galus : cal. calcaneum ; cub. 

 cuboid ; ctin. cuneiform ; 

 nav. navicular. 



The ccelome of the Rabbit differs 



from that of the Pigeon in being divided into two parts by 

 a transverse muscular partition, the diaphragm. The an- 

 terior part, or thorax, contains the heart and the roots of 

 the great vessels, the lungs and bronchi, and the posterior 



K K. 2 



