6a DESCRIPTIONS OF PREPARATIONS. 



and ischium fuse distally, and thus inclose an ileo-sciatic foramen. The 

 obturator foramen between the ischium and pubes is long and narrow, and 

 subdivided partially by the obturator process of the ischium. The femur 

 is remarkably short. The head is prominent, and its neck at right angles 

 to the main axis of the bone. The condyles are large and separated by 

 a deep patellar groove. The external one is typically subdivided, and its 

 outer subdivision plays between the tibio-tarsus and fibula. The former of 

 these two bones is the largest in the limb. It has proximally a cnemial 

 crest on the anterior surface, subdivided into a pro- and ecto-cnemial 

 process ; and distally there are two condyles formed from a cartilage in the 

 embryo which represents the proximal tarsalia astragalus and calcaneum. 

 Anteriorly and above these condyles a narrow bony bar confines the 

 extensor tendons of the toes. The fibula is slender and pointed distally. 

 The third section of the limb is the tarso-metatarsus, a compound bone 

 formed by the union of a bone representing the distal tarsalia to the heads 

 of the second, third, and fourth metatarsalia, of which the third is the 

 longest. Behind the tarsal element lies an ento-calcaneal process, the 

 attachment of the tendo Achillis, pierced and grooved by the flexor 

 tendons of the foot. The first metatarsal is small, incomplete proximally, 

 and united to the second by ligament. There are four digits in all the 

 first, or hallux, is turned inwards and backwards and carries two phalanges ; 

 the three remaining digits carry phalanges increasing successively in 

 number from three to five, the usual succession in Birds. The third is 

 the longest digit ; the fourth is so only in a few instances, e. g. Penguin, 

 Gannet, Pelican, &c. 



All the bones in the embryo contain marrow. The degree in which it is 

 replaced by air varies much. Apteryx, Penguin, small Songsters, have air only in 

 the skull : the Hornbill in every bone of the body. A membranous tube the 

 siphonium of Nitsche conveys air from the tympanic cavity to the lower jaw, as in 

 the Crocodile. This tube in the Raven, Thrush, &c. becomes bony. The 

 Cretaceous toothed birds had a pneumatic skeleton, as was probably the case in 

 the Dinosaurian Reptile, Coelurus. 



The outlines of the cranial bones can only be seen in a young skull. The 

 single condyle is made up, as in some Reptiles, by the basi- and ex-occipitals. The 

 parietals are short but wide. Two membrane bones the basi-temporals parts of 

 the parasphenoid, underlie the base of the skull, and the rostrum, or anterior part 

 of the parasphenoid, similarly underlies the mesethmoidal septum. The palatine 

 bones extend forwards to the maxilla and articulate behind with the rostrum. The 

 pterygoids articulate in front with the palatines and the basipterygoid processes of 

 the rostrum, while behind they diverge and articulate with the quadrate. The 

 maxillae have short palatal plates ' maxillo-palatine processes' which extend 

 inwards above the anterior end of the palatines. The squamosal and jugal are only 

 connected by ligament, not by bone, as in Mammalia. 



The Pigeon and Sandgrouse have no vomer, the Fowl has a pointed vomer 



