252 



cumscribed externally by the process already mentioned, which extends from the frontal to 

 the ethmoid ; the other by the corresponding process of the lacrymal. The foramen rotun- 

 dum is not only distinct, but is further apart from the foramen opticum than in any other 

 bird. The petrous bone projects internally in the form of a thin semicircular plate of bone, 

 commencing at the foramen ovale and extending backwards to the foramen auditorium inter- 

 num, which it overhangs : this plate gives attachment to the tentorium. There is not any 

 corresponding bony ridge developed from the upper wall of the cranium in the line of origin 

 of the falx, as in many of the Gallinaceous birds. The anterior or cerebral division of the 

 cranial cavity is larger in proportion to the posterior than in most other birds. 



The tympanic bone is of a subcompressed trihedral form, and sends forwards into the orbit 

 a longer and slenderer process than in the larger Struthionidee : its upper articular surface i 

 a transversely extended convex condyle, which plays in a corresponding cavity internal to the 

 base of the zygomatic process. The opposite extremity is expanded, and presents two distinct 

 articular convexities for the lower jaw, the inner one being the largest : above the external 

 convexity there is a small but deep depression for the reception of the deflected extremity of 

 the jugal bone. 



The posterior extremity of the pterygoid bone is securely wedged in between the orbital 

 process of the tympanic and the transverse process of the sphenoid : as it advances forwards 

 it expands, as in the other Struthionidee, into a thin plate of bone, which is bent upon itself 

 with its concavity turned inwards, and is continued by anchylosis into the palatine bones, so 

 that the limits between them cannot be defined. 



The palatine bones are in like manner confluent with the maxillaries. They are pierced 

 by two narrow elliptical posterior nasal foramina, about 3 lines in length, over which the 

 exterior margin of each palatine bone arches from without inwards, and these overarching 

 lamina; gradually approximate, as they advance forwards, and meet about one inch anterior 

 to the nasal foramina, from which an imperforate plate of bone, impressed with a narrow 

 median fissure, and composed of the confluent palatal processes of the maxillary and inter- 

 maxillary bones, is continued to the end of the beak. The limits between maxillary and 

 intermaxillary bones are indicated by two fine oblique lines, commencing at the outer margin 

 of the roof of the mouth, about 2^ inches from the apex of the beak. 



The jugal style, which iu the Ostrich may be separated in the full-grown bird into a zygo- 

 matic and malar portion, consists in the Apteryx of a single slender compressed twisted bone, 

 anchylosed with the maxillary bone in front, and terminated behind by an obtuse deflected 

 extremity, which is received into a corresponding vertical cavity in the upper part of the 

 outer process of the tympanic bone. By this mode of attachment the tympanic bone offers 

 increased resistance to the pressure transferred to it by the lower jaw, at the same time that 

 it gives additional strength to the upper mandible. 



The superior maxillary bone presents the singular form of a nearly perfectly flat elongated 

 triangular plate of bone, which is imperforate, and is continued by uninterrupted ossification 

 with the intermaxillary. The Rhea among the Struthionidee makes the nearest approach to 

 the Apteryx in the structure of this part of the skull ; but the maxillary plate is perforated 

 by large foramina, and sends upwards on each side a process to join the lacrymal. In the 

 Ibis the superior maxillary bones are in the form of slender round styles, having a wide inter- 



