TRITON 



93 



Distally, it articulates with the radius and ulna of the forearm. 

 The radius is the anterior of the two, i.e. preaxial. These 

 two bones in turn articulate with the bones of the wrist or 

 carpus, which is composed of seven small " carpal " bones. 

 The radiale (scaphoid) and ulnare (cuneiform) articulate with 

 the radius and ulna respectively. (Typically there are three 

 bones in this proximal row, the additional one being the inter- 

 medium (lunar) which here is fused with the ulnare.) Next, 

 there is a centrale, and the distal row of carpals is formed of 

 four bones. The bones of the fingers are the metacarpals, 

 and two or more phalanges, according to the finger. The 

 first finger has been lost, so the others are numbered 2 to 5. 

 The digital formula by which the number of phalanges is 

 expressed, is : o, 2, 2, 3, 2. 



Pelvic Limb and Girdle. — The pelvic girdle also consists 

 of a dorsal and two ventral elements. Dorsally, the ilium 

 leads from the acetabulum to the modified rib of the vertebra 

 forming the sacrum. The posterior ventral element is the 

 ischium : both ilium and ischium are bony. The anterior 

 element is the pubis which remains cartilaginous, and bears 

 another cartilaginous process akin to the sternum projecting 

 forwards. The ischium and pubis meet their fellows of the 

 opposite side in the middle line. 



Like the fore limb, the hind limb can be divided into three 

 parts : thigh, shank, and foot. The bone of the thigh is the 

 femur, which articulates with the acetabulum of the girdle. 

 Distally, it joins the tibia (preaxial) and fibula of the shank. 

 The ankle or tarsus is very similar to the wrist. The three 

 proximal tarsal bones are separate : tibiale, intermedium 

 (together possibly equivalent to the astragalus of higher forms), 

 and fibulare (calcaneum). The second row is represented by 

 the centrale (navicular), and the distal row by four bones. 

 The proximal bones of the toes are the metatarsals, bearing 

 the phalanges. The digital formula is 2, 2, 3, 3, 2. 



Alimentary System. — The floor of the mouth carries a 

 tongue, of which the hind edge is free.* Salivary glands are 



* This tongue has nothing to do with the similarly named structure in 

 Petromyzon. 



