94 LABORATORY MANUAL FOR VERTEBRATE ANATOMY 



The wrist is composed of a number of small bones, arranged in two transverse 

 rows. The proximal row consists of four pieces in the rabbit, three in the cat; 

 the distal row of five in the rabbit, four in the cat. Articulating with the distal 

 end of the radius is the large scapholunar in the cat, separated in the rabbit into 

 a medial navicular (radiate) and a lateral lunate bone (intermedium). Lateral 

 to the lunate portion or bone and articulating with the ulna is the triquetral bone 

 (ulnare). The pisiform is the element projecting prominently lateral to the 

 triquetral bone in the cat or behind it in the rabbit. The distal row of pieces 

 beginning at the medial side and proceeding laterally are: the greater multangular 

 (first carpale), the lesser multangular (second carpale), the central (centrale, missing 

 in the cat), the capitate (third carpale), and the hamate (fourth and fifth car pales 

 fused) . These carpales are situated at or near the proximal ends of their respec- 

 tive metacarpals. There are five metacarpals of which the first is very much 

 reduced, and five digits whose terminal phalanges support the horny claws. 



D. GENERAL SUMMARY OF THE GIRDLES, THE STERNUM, AND THE 

 PAIRED APPENDAGES 



i. The paired appendages probably represent remnants of a pair of continuous lateral fin 

 folds, supported by cartilaginous fin rays. 



2. The two girdles probably arose through the fusion in the median line of some of these 

 fin rays. 



3. The primitive girdles are bars or plates of cartilage in which subsequently ossification 

 occurred with the formation of cartilage bones. 



4. In each girdle three pairs of cartilage bones arise. These are ilium, pubis, and ischium 

 in the pelvic girdle; scapula, procoracoid, and coracoid in the same respective positions in the 

 pectoral girdle. 



5. The pelvic girdle after the three pairs of bones have arisen undergoes little change. In 

 birds and mammals the boundaries between the bones are lost by fusion, producing on each 

 side an innominate bone. There are never any membrane bones associated with the pelvic 

 girdle. 



6. The pelvic girdle is free in fishes but in all other vertebrates is firmly articulated or 

 ankylosed (i.e., immovably fused) to the sacrum by means of the sacral ribs. 



7. The pectoral girdle, on the other hand, exhibits many modifications among the 

 vertebrates and is further complicated by the addition of membrane bones. 



8. In the majority of the land vertebrates only two of the three cartilage bones of the 

 primitive girdle persist. The scapula is always present. One ventral element is generally 

 present, called the coracoid, and believed by some to be homologous with the coracoid in the 

 primitive girdle, by others to be homologous with the procoracoid. 



9. In all of the placental mammals the coracoid element is reduced to a vestige, the 

 coracoid process, borne on the scapula. 



10. The mammalian scapula is distinguished by the possession of a spine and of the cora- 

 coid process mentioned in paragraph 9. 



11. The membrane bones added to the pectoral girdle vary in different forms, but in living 

 land vertebrates usually consist of paired clavicles and a median unpaired interclavicle. 



12. The pectoral girdle is very rarely connnected with the vertebral column by an articula- 

 tion or ankylosis. 



