OSSEOUS SYSTEM. 71 



the Owls, the Pigeons, Snipes, Goatsuckers, and birds of the Duck 

 kind, and contributes to the movement of the superior maxillary arch. 

 The temporal bone consists of a cranial portion which encloses the 

 orga-n of hearing, and is formed by the early coalescence of the pe- 

 trous, squamous, and mastoid portions ; the squamous frequently gives 

 off an inferior spine-shaped zygomatic process, not connected, how- 

 ever, with the jugal bone ; the mastoid process is but slighty devel- 

 oped, and there is moreover an articular portion, the tympanic or os 

 quadratum. This bone, which is free, and wanting in the Mamma- 

 lia, occurs constantly in the other Vertebrata, where it often con- 

 sists of several portions ; it very generally projects superiorly into 

 two processes, the posterior one of which, the largest, articulates by 

 a rounded head with the cranium, while the anterior remains free. 

 Inferiorly it articulates with the lower jaw, inferiorly and externally 

 with the jugal bone, inferiorly and posteriorly with the lower wings 

 of the sphenoid. Laterally, and in the direction inward, the os 

 quadratum gives off a peculiar tympanic process, which helps to 

 form the posterior wall of the tympanic cavity, and partakes in the 

 movement of the upper jaw. This process exhibits no inconsider- 

 able differences in the several orders. The parietal bone, origi- 

 nally consisting of two halves, abuts anteriorly against the frontal, 

 which is also double in early life. The latter has often concave de- 

 pressions or deep grooves, as in the Gulls and many other Aquatic 

 birds, for the reception of the nasal glands, which here lie upon the 

 edge of the orbital cavity. The ethmoid is occasionally present only 

 as a single perpendicular plate, which, with the sphenoid, forms 

 either the closed or more or less perforated partition of the orbits. 

 This partition is frequently, in nearly allied birds, completely bony, 

 as in the Stork, or very perforated and membranous, as in the Heron. 

 The ethmoid, however, frequently exhibits traces of lateral portions, 

 as in the Passeres, e. g. Corvus, the Rapaces, and many Scansores, 

 where they are more strongly developed, and abut against the lacry- 

 mal bone. 



As regards the Facial bones, an intermaxillary bone of mostly 

 large size and single (rarely, as in the Gallinae and Snipes, of small 

 or minute size), forms the principal part of the upper bill, and 

 exhibits great diversities of form. Superiorly and posteriorly it is 

 slit for the reception of the nasal cavities, and sends usually a long, 

 narrow, flattened process between the nasal bones. In the Parrots 

 the intermaxillary bone is merely united by ligament to the skull, 

 and is therefore very moveable, while in other cases the union is 



