CHAPTER V 



THE LIMBS 



Two pairs of limbs are almost always present in reptiles, composed^ 

 as in mammals, of four analogous segments: the arm and thigh bones, 

 conveniently called propodials; the forearm and leg bones, or epi- 

 podials; the wrist and ankle bones, or mesopodials; the manus and 

 peSj composed of metacarpals and metatarsals, or metapodials; and 

 a variable number of finger and toe bones, known as phalanges. 



The limbs are best understood and described as though directed 

 outward from the long axis of the body (Fig. 128), the palms of the 

 hands and soles of the feet turned downward or to the ventral side, 

 the epipodials parallel, the thumb or pollex, and the big toe or hallux^ 

 on the anterior or preaxial side, the little finger and little toe on the 

 posterior or postaxial side. The terms outer and inner are often ap- 

 plied to the anterior extremity, as though directed backward in the 

 axis of the body, the thumb on the outer side. The hind extremities 

 are sometimes described as though parallel with the long axis of the 

 body, with the big toe on the inner side. As the hallux is analogous 

 with the pollex, this nomenclature places them on the opposite sides 

 and should not be used for any vertebrates. 



The fore and hind Hmbs of terrestrial reptiles are of approximately 

 equal length, the hind pair the longer. In aquatic reptiles [e.g., 

 ichthyosaurs, mosasaurs] the front pair are often the larger, and 

 usually the longer; in volant reptiles [pterosaurs] they are much 

 longer than the hind pair. In bipedal reptiles [e.g., later Theropoda] 

 or those usually assuming this posture in locomotion, they are smaller 

 or very much smaller. In climbing and cursorial reptiles the limbs 

 are more or less, sometimes very much, elongated and slender (Fig. 

 155). The digits of fleet, crawHng reptiles are long; those of the more 

 upright-walking kinds (Figs. 145, 141 i), in which the digits of the 

 two sides are brought more nearly parallel to each other, are short. 

 The articular surfaces of the limb joints of aquatic reptiles (Figs. 

 149, 158) are poorly developed, unextensive, and more or less carti- 

 laginous. 



155 



