908 



SUB-KINGDOM VERTEBRATA. 



the outer or inner epicondyle. When placed above the outer or 

 radial epicondyle this foramen is termed ectepicondylar, and when 

 above the inner or ulnar epicondyle entepicondylar. The proximal 

 extremity of the ulna is often produced into an olecranon (fig. 1300), 

 which projects behind the end of the humerus. The distal ex- 

 tremity of the tibia in certain Sauropsida develops from its anterior 

 aspect a ridge or process known as the cnemial crest ; while the 

 deltoid crest or ridge is a prominence situated below the head of the 

 humerus on the radial side, to which the attention of the palaeon- 

 tologist is not unfrequently directed. Finally, the patella is a so- 

 called sesamoid bone developed in the tendon of a muscle passing 

 over the pulley-like surface or trochlea on the anterior aspect of the 

 distal extremity of the femur. 



Since the limbs of Fishes differ considerably from the higher type 

 of structure noticed above, their consideration may be deferred till 

 we come to that class. Before, however, leaving the subject of 

 limbs, it should be observed that it is often convenient to allude to 

 the corresponding or homologous sides of the fore and hind limbs 

 by a single term. If, then, we imagine the limbs extended more or 

 less nearly at right angles to the axis of the body (as on the left 

 side of fig. 814), with the palm of the hand and the sole of the 

 foot directed to the front or ventral aspect, the middle digit of 

 each limb will be axial, when the pollex 

 and radius of the pectoral, and the homo- 

 logous hallux and tibia of the pelvic 

 limb, will be obviously preaxial ; while 

 the fifth digit of each limb, together with 

 the ulna and the fibula, will be postaxial. 

 The whole of the radial and tibial sides of 

 the limbs will accordingly be known as the 

 preaxial, and the ulnar and fibular as the 

 postaxial border. 



The remaining parts of the skeleton 

 comprise the pectoral and pelvic girdles, by 

 which the corresponding limbs are respec- 

 tively connected with the trunk, and of 

 which the relative positions are shown in 

 fig. 818. The pectoral arch is never con- 

 nected by means of ribs with the verte- 

 bras, and primitively consists of three main 

 bones developed in cartilage. On the 

 dorsal aspect of the body we have the 

 upper bone or scapula (fig. 830, s) ; while on the ventral side there 

 are two parallel bones (fig. 974), the anterior of which is termed 



Fig. 830. — Lateral aspect of 

 the cartilage bones of the left 

 side of the pectoral girdle of a 

 Lizard {Iguana), s, Scapula ; 

 ■ni.sc, Mesoscapular process of 

 do. ; cor, Coracoid ; p.cor, Pre- 

 coracoidal process of do. ; m.cor, 

 Mesocoracoidal process of do. ; 

 for, Foramen of do. ; gl, Glenoid 

 cavity. 



