364 



ZOOLOGY 



SECT. 



pre-axially, into an outstanding step-like process. The study of 

 development shows that this bone is formed by the union of the 



distal carpals with three metacarpals 

 (Fig. 976), the second and third of 

 which are the two rod-like portions of 

 the bone, the first the step-like pro- 

 jection. Articulating with the first 

 metacarpal is a single pointed phalanx 

 (ph.l)\ the second metacarpal bears 

 two phalanges, the proximal one (ph. 2') 

 produced postaxially into a flange, the 

 distal one (ph. 2") pointed ; the third 

 metacarpal bears a single pointed 

 phalanx (ph. 3). 



The pelvic girdle (Fig. 968) resembles 

 that of no other vertebrate with the 

 exception of some Dinosaurs. The 

 ilium (il.) is an immense bone, attached 

 by fibrous union with the whole of 

 the syn-sacrum and becoming anky- 

 losed with it in the adult. It is 

 divisible into prz-acdcibular and post- 

 acetabidar portions of approximately 

 equal size. As usual it furnishes the 

 dorsal portion of the acetabulum, and 



on the posterior edge of that cavity is produced into a process, 

 the antitrochanter (a.tr.} which works against the trochanter, a 

 process of the femur. The ventral portion of the acetabulum 

 is furnished in about equal proportions by the pubis and ischium 

 (Fig. 977) : it is not 

 completely closed by 

 bone, but is perforated 

 by an aperture covered 

 by membrane in the 

 recent state. Both 

 pubis and ischium are 

 directed sharply back- 

 wards from their dorsal 

 or acetabular ends. The 

 ischium (is.) is a broad 

 bone, ankylosed pos- 

 teriorly with the ilium, 

 and separated from it 

 in front by an ischiatic 

 foramen (is.for.). The 



pubis (pu.) is a slender, curved rod, parallel with the ventral edge 

 of the ischium, and separated from it by an obturator notch (obt.n.). 



FIG. 976. Columba livia. Left 



manus of a nestling. The car- 

 tilaginous parts are dotted. 

 cp. 1, radiate ; cp. %, ulnare ; 

 mcp. 1, 2, 3, metacarpals ; ph. 1, 

 phalanx of first digit ; ph. 2, 

 ph. 2', phalanges of second digit ; 

 ph. 3, phalanx of third digit ; 

 . ra. radius ; ul. ulna. (From 

 Parker's Zootomy.) 



il 



a.tr 



pu 



FIG. 9 



nest- 



Columba livia. Left innominate of 

 ling. The cartilage is dotted, ac. acetabulum ; a. tr. 

 anti-trochanter ; il. pre-acetabular ; and il'. post-aceta- 

 bular portion of ilium ; is. ischium ; i. s. f. ischiatic 

 foramen ; ob. f. obturator notch ; pu. pubis. (From 

 Parker's Zootomy.) 



