OSTEOLOGY OF BIRDS 



17 



thrown out to support it. In all these birds a marked depression 

 occurs just anterior to this articulation, and immediately above the 

 inner mandibular condyle ; it is best seen in the Californian vulture, 

 and is hardly observable in C a t h a r t e s a . s e p t e n t r i o n a 1 i s. 

 The condylar surface on the underside of the quadrate, intended 

 for the lower jaw, is, as usual in so many birds, divided into two 

 irregular, undulating facets, separated by a middepression ; the long 

 diameter of the whole being situated transversely. Quite a marked 

 constriction exists between the mastoid and orbital processes and the 

 mandibular end, made apparent by the enlargement of the latter to 

 support the mandibular condyles. The portion bearing the outer 

 condyle is produced outward, forward and upward, as a cylindrical, 

 stout apophysis, having in its extremity the deep, conical pitlet for 

 the reception of the process upon the end of the zygoma. 



While we are once more within the neighborhood of the orbital 

 cavity, there is yet one point to be noticed in reference to it, and 

 it has to do with that part of the cranium through which the nasal 

 nerves pass. Cathartes a.septentrionalis in its cran- 

 ium offers a covered, osseous, mesial conduit for its first pair of 

 cranial nerves as they pass from the rhinencephalon to the rhinal 

 chamber. Through the presence of vacuities, in subadult birds, this 

 may be more or less open on its sides in the orbital cavities, but in 

 older individuals, we rarely find more than a pair of small foramina 

 in the lateral walls of this 'bony passage. 



By an extension upward of the interorbital septum in Catharista 

 and Gymnogyps the passage is rendered double, so that the nerve 

 of either side has a tube for its own accommodation. Catharista 

 often has the outer walls of this passage quite deficient, while its 

 mesial septum is nearly entire. All Cathartidae have in the back 

 part of the roof of the orbit the usual circular and small foramen 

 for the orbital vein, with a shallow groove leading forward from 

 it. In Neophron it is like it is in the Falconidae, that is, an open 

 channel is provided for the nasal nerves. 



The pterygoids are horizontally compressed and twisted at their 

 posterior ends in the Carrion crow. They exhibit upon their mesial 

 edges the elongate facets for the pteryapophysial processes of the 

 basisphenoid ; these facets are toward the anterior and broader 

 ends of the bones. As we have said, the posterior extremities of 

 the pterygoids are constricted and twisted upon themselves, so as 

 to bring their articular facets to meet those (that were described) 

 for their reception upon the quadrates, while the anterior ends are 



