212 



Class AVES. 



CHIEF CHARACTERISTICS OF THE SKELETON, AND TEXTURE OF 



THE BONES, OF BIRDS. 



1101. The right moiety of the vertically bisected cranium of an Albatros (Diome- 

 d<ea exulans). 



It shows the ivory-like whiteness and compactness of the osseous tissue, and the loose open 

 cancellous structure of the bones. Air is admitted into these cancelli partly, as may be seen, 

 from the nasal passages, and partly from the tympanic cavity which receives it from the 

 eustachian tube ; from the latter source the proper bones of the cranium receive their air. 

 Some of the characteristic features hi the composition of the skull of birds may here be 

 noticed : as, for example, the obliteration of all the ordinary sutures of the cranium, except 

 those which unite the tympanic bone, as (auditory process of the temporal), to the mastoid, s 

 (mastoid process of the temporal) ; and that which unites the pterygoid, 23 (pterygoid pro- 

 cess of the sphenoid), to the basisphenoid, 5 (basilar process of the sphenoid) ; which sutures 

 are speedily obliterated in the Human Subject. The premaxillary is confluent with the nasal 

 and with the maxillary ; the nasal being confluent with the frontal and the maxillary with 

 the jugal. The jugal and squamosal are also confluent, and form a long zygomatic style in 

 all birds, connected at the hinder extremity by a moveable glenoid joint to the outer and 

 lower part of the tympanic. The pterygoid articulates, in like manner, with the inner and 

 lower part of the tympanic, the movements of which are thus communicated to the upper 

 mandible, so far as the junction of the nasal with the frontal admits of such independent 

 motion. 



Presented by Prof. Owen, F.R.S. 



1 102. The right moiety of the vertically bisected cranium of a Gannet (Sula Bassana). 



It shows the moveable articulation between the nasal and frontal by which the upper jaw 

 can be raised. Both facial and cranial bones show the same open cancello-reticulate texture 

 for the reception of air as in the Albatros. 



Presented by Prof. Owen, F.R.S. 



1103. A longitudinal section of a cervical vertebra of an Ostrich (Struthio Camelus). 



It shows its open cancellous texture, and the orifice which admitted air therein from a con- 

 tiguous cervical air-cell. In this specimen may be noticed what appears to be a perforated 

 transverse process, but the nature of which is shown in the following specimen. 



Hunterian. 



