414 THE VERTEBRATE SKELETON. 



tibia and articulates by its proximal end with the head of the 

 tibia, and by its distal end with the calcaneum. Its shaft 

 and proximal end ossify from one centre, and its distal end 

 from a second. 



The Pes. 



The structure of the pes corresponds closely with that of 

 the manus. It is divided into : 



a. The tarsus or ankle formed of a group of small 

 bones. 



6. The foot, which includes, firstly, some elongated bones, 

 the metatarsals, forming what corresponds to the sole of 

 the foot, and secondly the phalanges, which form the toes. 



The Tarsus. The tarsus of the dog consists of seven bones 

 arranged in two rows, of two and four respectively, with a 

 centrale between them. The two bones of the proximal row 

 are the astragalus and calcaneum. 



The astragalus (fig. 80, 10) corresponds to the fused 

 tibiale and intermedium of the typical tarsus. Its proximal 

 end is much wider than its distal end, and forms a large 

 rounded condyle articulating with the tibia, while its pos- 

 terior end meets the navicular. It lies to the dorsal side of 

 the foot. 



The calcaneum (fibulare) (fig. 80, 11), the thickest bone 

 in the pes, lies somewhat behind, and to the outer side of the 

 astragalus. It articulates with the astragalus and fibula, and 

 is drawn out behind into a long rounded process, which forms 

 the heel, and is in the young animal terminated by an epi- 

 physis. Between the proximal and distal rows of tarsals is 

 the navicular (centrale) (fig. 80, 12), a somewhat flattened 

 and square bone articulating with the astragalus. 



The distal row of tarsals consists of four bones. The 

 internal cuneiform (tarsale 1) is a smooth flattened bone 

 lying to the inner side of the foot; it articulates with the 



