1874.] ANATOMY OF THE PARROTS. 593 



able but much involved field for work, which has only been entered 

 upon by the illustrious Nitzsch. 



Referring back to the characterizing features of the existing species 

 whose internal structure has been noted, it will be seen that none 

 has as yet been found with a conformation exactly similar to that 

 of the above-described ancestral bird ; in other words, no existing 

 Parrot has been seen with two normal carotids, an ambiens muscle, 

 a furcula, and an oil-gland. By more than a single way, however, 

 this condition, with only one exceptional character, is found to exist. 

 For instance, the fourth combinationabove given, in which theambiens, 

 furcula, and oil-gland are present at the same time that the carotids 

 are abnormal (the left being superficial), agrees with the type except 

 in one point — the disposition of the carotid arteries. Again, in the 

 first of the combinations the only deviation from the type consists in 

 the absence of the ambiens muscle. 



These two different directions of variation must therefore have 

 formed the secondary stems from which the more specialized genera 

 subsequently sprang. In other words, the main stem must have 

 given rise to two, in one of which the carotids remained normal, 

 whilst in the other the left became superficial. The following are 

 the genera as they will thus appear : — 



Genera in which the left carotid Genera in which the left carotid 



has remained normal. lias become superficial. 



(Pal^eornithid-e.) (Psittacid^e.) 



Agapornis. Ara. 



Aprosmictus. Bolborhyyichus . 



Cacatua. Brotogerys. 



Calopsitta. Caica. 



Calyptorhynchus. Chrysotis. 



Eclectus. Conurus. 



Eolophus. Coracopsis. 



Eos. Cyanorhamphus. 



Euphema. Lathamus. 



Geopsittacus. Nestor. 



Loriculus. Pionus. 



Lorius. Platycercus. 



Melopsittacus. Pyocephalus. 



Palceornis. Psephotus. 



Prioniturus. Psittacus. 



Psittinus. Psittacula. 



Stringops. Pyrrhulopsis. 



Tanygnathus. Pyrrhura. 

 Trichoglossus. 



Each of these secondary types must have then become a centre 

 for variation in itself. From the 4 th combination, in which only 

 the carotids are peculiar, sprang the 5th, Cth, and 7th, with the 

 ambiens deficient, just in the same way that the 1st, 2nd, and 3rd 

 combinations originated from the ancestral form by the same process 

 of reduction. The loss of the furcula and of the oil-gland (though 



