86o 



SKELETON 



much aborted digit seems in embryonic Ostriches to bear a claw 

 (page 89). In the Sphenisci the pollex is more or less completely 

 fused with the index, which latter is made up of two long pha- 

 langes, while the third digit consists of one long phalanx. Casiuirius, 

 Dromseus and Apteryx retain only the index, the first and third 

 disiits beinii; either lost or reduced to insi2;nificant traces.^ 



The Pelvic Arch is the portion of the pelvis (page 703) 

 which is made up of the ilium (page 458), ischium (page 460) and 

 OS pubis (page 748), the last three being paired bones which meet 

 on each side at the acetabulum or cup that receives the head of the 

 FEMUR (page 248), coalescing with each other at an early stage. 

 The ilium may be conveniently divided into a praeacetabular and 

 a postacetabular part, the relative proportions of which afford some 

 useful characters ; thus in the Gallinai they are nearly equal, but 



Common Fowl, Embryo and Chick. 

 Ac. Acetabulum ; F.ls. Foramen iscliiadicum ; Pr.p. Processus pectinealis. 



in the Accipitres the anterior is longest, while in Col//mhis, where 

 most of the pelvis is drawn out backward, it is only half the length 

 of the posterior. To the inner surface of the ilium, and in most 

 cases near its ventral margin, are attached the lateral processes of 

 the cruro-sacral vertebrae (page 855), while near its dorsal rim is 

 attached all the rest of the sacrum. The outer surface of the 

 praeacetabular portion forms a broad vertical blade with a more or 

 less deep concavity which serves for the origin of the external 

 iliac muscles (often mistakenly called glutaeal). In rare cases the 

 right and left pr?eacetabular portions fuse with each other along 

 their dorsal edge above the spinous processes of the neighbour- 

 ing vertebrae and enclose a canal on each side. In front of the 



^ As an appendix to the account of tliis part of the Skeleton, mention should 

 here be made of the Sesamoid Bones. These are not disconnected portions of 

 the framework, but cartilaginous or osseous formations either within the 

 capsules of joints, as the htu/irro-scap^dar bone in the capsule of the joint of 

 that name, or within the inserting tendons of muscles, as the imtella of the 

 knee and the ■patella ulaaris of the Sphenisci, and osseous or cartilaginous nodules 

 in the tendons of the long muscles of the toes, of the t/msc. extensor inetacarpi 

 radialis and of the nuisc. propatagialis. 



