OSSEOUS SYSTEM. 73 



perpendicular bony plate. The jugal bone, which is throughout the 

 class very long, slender, and flattened, consists of two pieces, and 

 is united posteriorly to the os quadraturn by fibro-cartilage, anteriorly 

 with the jugal process of the superior maxillary by suture, forming 

 nearly always a straight bridge of bone parallel with the lower jaw. 

 It is only in the Goatsucker (Caprimulgus) that the jugal bone is 

 arched in the direction outward to conform with the similarly pro- 

 jecting posterior piece of the lower jaw. In other instances the 

 zygomatic arch is very short and strong, as in Buceros, or very slen- 

 der, as in the Snipes. 



The Lower Jaw consists of a single anterior and five pairs of pos- 

 terior pieces, perfectly analogous to those in the lower jaw of the 

 Amphibia. They soon, however, coalesce, the anterior pretty firmly, 

 the posterior pieces completely. Instead of the articulating condyle, 

 there is found, as in all the Yertebrata below the Mammalia, an ar- 

 ticulating cavity for the reception of the os quadratum, and which 

 gives off internally and superiorly a kind of coronoid process, and in 

 the direction backward a frequently long and very much developed 

 process, as is seen particularly in the Gallinae, e. g. the Grouse. Mi- 

 nor differences also frequently occur ; thus in Cypselus the lower 

 jaw is in the form of a very narrow and slender arch, while in the 

 Parrots it is formed of deep perpendicular bony walls ; in both the 

 processes are wanting. In the Crow and most Passeres the poste- 

 rior half of the lower jaw is perforated by a large opening. It is re- 

 markable that in birds the whole apparatus of the superior maxilla 

 (supporting the upper Mandible) admits generally of a slight, occa- 

 sionally even a considerable degree of motion, in the direction up- 

 ward and forward, which is effected by the moveable connexion pos- 

 teriorly of the palatal, sphenoid, jugal, and quadratal bones. 



The different portions of the Vertebral Column in birds exhibit 

 several peculiar and remarkable arrangements. The number of the 

 vertebrae not only varies very considerably in the orders, but^also 

 among the genera and species, and even in individuals of the same 

 species ; the Swan, for example, has generally 23, but frequently 

 also 24, cervical vertebrae. The relative numbers of the vertebrae 

 are, however, in general more constant than in the Amphibia. The 

 cervical vertebrae are always more numerous than in the Mammalia ; 

 as a rule, there are from 11 12 (rarely only 9 or 10), as in most 

 Rapaces, Passeres, and Scansores birds; 13 15 in the Gallinae, 

 16 19 in the long-necked Grallae and Palmipedes, as in the Stork, 

 Crane, Heron, and also in the Ostrich and Cassowary ; 23 24, as in 



