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Show 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 combination above given, in which the ambiens, 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. has become superficial. (PAL^EORNITHID^E.) (PSITTACID^E.) Agapornis. Ara. Aprosmictus. Bolborhynchus. Cacatua. Brotogerys. Calopsitta. Ca'ica. Calyptorhynchus. Chrysotis. Eclectus. Conurus. Eolophus. Coracopsis. Eos. Cyanorhamphus. Euphema. Lathamus. Geopsittacus. Nestor. Loriculus. Pionus. Lorius. Platycercus. Melopsittacus. Pceocephalus. Palaornis. 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 4th combination, in which only the carotids are peculiar, sprang the 5th, 6th, 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 |