ANATOMY OF VERTEBRATES. 



trihedral for a subcompressed form, and is more slender than 

 the ischium. The shortest pubis is seen in certain Eagles, 

 in which it terminates after forming the lower boundary of the 

 obturator foramen; its extremity there projecting freely, as in 

 fig. 23, d, or being joined by ligament to the ischium, as in the 

 Harpy Eagle, in which it is an inch in length, whilst the ilium is 



six inches long. The opposite ex- 

 treme may be seen in the Guillemots 

 and Grebes ; and in the latter the 

 pubic styles diverge from the aceta- 

 bula with a slight outward bend, the 

 interspace of their extremities being 

 twice the breadth of the fore part of 

 the pehds : they are usually longer 

 than the ischia, figs. 24 and 34 ; but 

 in the Apteryx they equal that bone 

 in length, and in the Emeu they are 

 shorter. The pubis coalesces with the 

 ilium and ischium at the acetabulum ; 

 usually again mth the ischium, as at 

 k, fig. 22, to close the tendinal fora- 

 men, and, in some birds, a third time 

 Avith the end of the ischium, as in 

 fig. 24, to circumscribe the obtura- 

 tor vacuity, o. In Doves, the pubis 

 after uniting with the ischium to close 

 the tendinal foramen, extends back- 

 Avard parallel with and close to its lower 

 margin, sometimes contracting a bony 

 union therewith and obliterating the 

 ^ obturator ' interspace. The pubic 

 bones as they extend backward in the 

 Apteryx are nearly parallel ; in the 

 EmeUi Neomorpha, Cassicus^ Podiceps, they diverge. In most 

 birds the fore part of the acetabular portion of the pubis forms 

 a ridge or tuberosity, figs. 24, m, and 22, §'; in some it is 

 produced to a greater extent (^Geococcyx, Corythaix, Tinamus, 

 Oreophasis). 



In accordance with the above-stated differences in the form and 

 proportions of sacrum, ilium, ischium, and pubis, the pelvis of the 

 Bird varies in its general form and proportions. From that of all 

 cold-blooded Vertebrates it differs in the greater number of ver- 

 tebral segments entering into its composition, and in their bony 



Pelvis of Ostricl 



