AVES. 



287 



bone of the pelvis which comes in con- 

 tact with the vertebral column, and it ex- 

 tends from the posterior dorsal vertebrae along 

 the whole of the sacrum, to which it is early 

 united by anchylosis. At its posterior extre- 

 mity it is expanded laterally and becomes 

 anchylosed with the ischium (c,fig. 131) pos- 

 terior to the ischiadic notch (e,Jig- 131) which 

 is thus converted into a foramen. 



The ilium is of a considerable size, of an 

 elongated form, expanded at its extremities and 

 contracted in the middle ; the anterior expan- 

 sion is concave externally, the posterior on the 

 contrary convex. Besides being anchylosed 

 with the ischium and sacrum, the spinous and 

 transverse processes of one or two posterior 

 dorsal vertebrae are commonly joined to it by 

 bony union. In the Penguins, however, where 

 the posterior extremities are ill adapted for 

 su pporting the body in progressive motion 

 on land, the ilium appears at no time to be 

 anchylosed with any part of the vertebral co- 

 lumn. 



The os pnbis (^ fig. 125, b b, Jig. 131 ) does 

 not extend to meet its fellow on the mesial 

 line, but is commonly directed backwards like 

 a long bent styliform process (3, Jig. 134), 

 adapted to allow a safe passage to the large 

 and fragile eggs. In general it unites with the 

 ischium so as to complete the obturator fora- 

 men (J\ fig. 131), behind which another fo- 

 ramen is occasionally formed by a second 

 union with the ischium, as is seen in the Hum- 

 ming-bird ; while in other Birds, as the Stork, 

 it is only united to the ischium at the cotyloid 

 foramen, and the obturator hole communicates 

 with a long fissure and is completed posteri- 

 orly by ligament only. The cotyloid cavity for 

 the head of the thigh-bone is always incomplete 

 at its posterior or internal part, which is closed 

 in the recent state by a strong aponeurosis. 



The ischium (c, jig. 131) is a small elon- 

 gated bone, slightly convex externally, ex- 

 tending from the acetabulum backwards, pa- 

 rallel with the ilium. 



In the Struthious Birds the pelvis is pro- 

 portionally very long, but narrow ; the ossa 

 innominata cover the whole of the sacrum, 

 meeting and joining above that part like the 

 roof of a dwelling. In the Rhea, or Ame- 

 rican Ostrich, the ischiadic bones meet below 

 the sacrum, where they are united for a con- 

 siderable extent by a symphysis, so that the 

 sacrum is closely surrounded, and in fact its 

 place is almost supplied by the ossa inno- 

 minata, for the development of the included 

 vertebrae is in consequence so much impeded, 

 that they can scarcely be detected at this 

 part; beyond which, however, the coccygeal 

 vertebrae suddenly resume their ordinary mag- 

 nitude. This union of the ischia does not 

 take place in the other Struthious birds ; but 

 the Ostrich presents the remarkable exception, 

 among Birds, of the completion of the pelvic 

 circle by the anchyloses of the pubic bones at 

 their inferior extremities. 



The femur (Q,frg. 125, g,fig. 131) is a short 

 cylindrical bone, deviating from the straight line 



by a very slight anterior convexity. The head 

 is a small hemisphere; joined, without the in- 

 tervention of a neck, at a right angle, to the 

 shaft of the bone : it presents at its upper part, 

 a considerable depression for the attachment of 

 the round ligament. The single large trochan- 

 ter generally rises above the articular eminence, 

 and is continuous with the outer side of the 

 shaft. The orifice for the admission of air 

 into the bone is situated anterior to this ca- 

 vity. The femur is most readily characterised 

 by the form of its lower extremity : this pre- 

 sents as usual two condyles, the inner one cor- 

 responding to the tibia, the outer one, which 

 is the largest and the longest, resting both upon 

 the tibia and fibula; upon this condyle a semi- 

 circular rounded eminence is observed extend- 

 ing from the front to the back part, and being 

 lost in a depression at both extremities; the 

 result of this structure is to put the external 

 lateral ligament upon the stretch when the 

 fibula is passing over the middle of the condyle, 

 and that ligament, being elastic, pulls the 

 fibula into the cavity in which the ridge termi- 

 nates, with a jerk whether the motion be that 

 of flexion or extension, in either of which con- 

 ditions the leg is by this structure the more 

 firmly locked to the thigh. It has been denied 

 that the spring-joint ever exists at the knee, and 

 it is probable that all birds do not possess the 

 requisite structure in the same perfection ; but 

 a common indigenous species, the Water-hen, 

 (Gullinula Chloropus) affords a good example 

 of the beautiful mechanism in question. The 

 femur attains its greatest development in the 

 Ostrich ; but in this species it is short in com- 

 parison to the other bones of the leg, the length 

 of which in the Stilt-bird and other Waders is 

 attained solely by the elongation of the tibia 

 and metatarsus. 



The tibia (J%.125,M,./Zg.l31) is the prin- 

 cipal bone of the leg thejibula (x,Jig- 125, ', 

 Jig. 131) appearing as a mere styliform process 

 tapering to a point below, and anchylosed for a 

 greater or less extent to the tibia. The tibia is 

 of a triangular form, especially at its enlarged 

 superior extremity, the articular surface of which 

 is unequal, being flat internally, convex at the 

 centre, and concave externally and in front. 

 The inferior articular surface of the tibia forms 

 a considerable transverse trochlea, above which 

 anteriorly there is a deep depression. In ge- 

 neral an osseous bridge extends transversely 

 across this depression, converting it into a 

 foramen through which the tendon of the Exten- 

 sor communis digitorum passes. 



In the Divers, Grebes, Guillemots, and 

 Albatrosses the middle and internal crests of the 

 tibia unite superiorly and are extended up- 

 wards into a long pointed process (k, Jig. 131) 

 directed inwards and forwards, anterior to, but 

 not supplying the place of, the patella, (I, Jig. 

 131) which will be always found as a distinct 

 bone behind this process. The process is most 

 developed in the genus Colymbus, and affords 

 extensive attachments by way of insertion to 

 the extensors of the tibia, and by way of origin 

 to the extensors of the metatarsus ; by means 



