88 LABORATORY MANUAL FOR VERTEBRATE ANATOMY 



bone, the humerus, a middle segment— the forearm or anlibrachium, containing two bones: 

 a preaxial radius and a postaxial ulna, and a distal segment— the hand or manus. The hand 

 is subdivided into three parts: the wrist, the palm, and the fingers. The wrist is primitively 

 composed of nine or ten bones in three rows : a proximal row of three, named the radiale, the inter- 

 medium, and the ulnare; a middle row of one or two centrales; and a distal row of five 



d a 



Fig. 20. — Pectoral girdles of some vertebrates. A, side view of half of the pectoral girdle of an 

 extinct amphibian, Cacops, belonging to the Stegocephala; note presence of the cleithrum b. B, ventral 

 view of both halves of the pectoral girdle of a very ancient extinct reptile, Seymouria, belonging to the 

 Cotylosauria, illustrating the complete generalized pectoral girdle; note presence of both coracoid and 

 procoracoid. C, ventral view of both halves of the pectoral girdle of a modern reptile, a lizard; note 

 loss of one of the coracoid bones. D, ventral view of both halves of the pectoral girdle of a monotreme 

 mammal, the duckbill, Ornithorhynehus, illustrating the most primitive pectoral girdle found amongpresent 

 mammals; note persistence of the coracoid and interclavicle, similar to reptiles. E, ventral view of 

 one-half of the pectoral girdle of an ape; note absence of the interclavicle and reduction of the coracoid 

 to the coracoid process/. Cartilage, close stippling; cartilage bones, open stippling; membrane bones, 

 blank, a, coracoscapula; b, cleithrum; c, clavicle; d, interclavicle; c, scapula; /, coracoid (coracoid 

 process in E); g, procoracoid; //, epicoracoid cartilage; i, glenoid fossa; j, spine of the scapula. (.-1 

 from WiUiston's Water Reptiles of the Past and Present, University of Chicago Press; B, after WiUiston; 

 C from Reynolds' The Vertebrate Skeleton, courtesy of the Macmillan Company; D from Wiedersheim's 

 : Anatomy of Vertebrates, courtesy of the Macmillan Company.) 



carpales. The palm is composed of five elongated metacarpals and the fingers of phalanges 

 whose numbers are primitively the same as in the case of the toes (see Fig. 27). 



3. The pectoral girdle and pectoral fin of elasmobranchs. — In these fish 

 we find the pectoral girdle in a primitive condition, resembling that of the pelvic 

 girdle. It is a curved cartilage almost completely encircling the anterior part of 



