1868.J PROF. HUXLKY ON THE ALECTOROMORPHi*;. . 295 



author is, in fact, a perfect mine of information for those who do 

 not mind the trouble of digging, and I shall frequently have to ex- 

 press my concurrence with the views therein expressed. 



But, in attempting to discover the affinities of Opisthocomus, I 

 have been led to believe that a good deal yet remains to be done in 

 the way of defining the limits of the Alectoromorphm, the value of 

 the subdivisions of the group, and the relation of these subdivisions 

 to zoogeography, 



I propose to make a contribution towards these objects in the 

 present paper by discussing: — 1st, the proper limits of the group 

 Alectoromorphce and of its subdivisions ; 2ndly, the relations of 

 sundry outlying forms, commonly regarded as Gallinaceous birds, 

 with the Alectoromorphce and adjacent groups ; 3rdly, the geogra- 

 phical distribution of the Alectoromorphce in relation to geographical 

 distribution generally. 



I. The proper limits of the Group Alectoromorphae and of its 



subdivisions. 



In my paper "On the Classification of Birds"* I have included 

 the PteroclidcB and the TurnicAdce with the PhasianidcB, Megapo- 

 didce, and Cracidce in one division, Alectoromorphce, though the 

 aberrant characters of the Turnicidce and Pteroclidce are fully re- 

 cognized. I am now convinced that it will be much more convenient 

 to restrict the title of Alectoromorphce to the three latter groups, 

 which agree with one another, and differ from the other two in the 

 following osteological characters : — 



1. The last cervical vertebra and the anterior dorsals are always 

 ankylosed together in the adult. One of the posterior dorsals 

 (generally, if not always, the penultimate) remains free, while the 

 hindermost becomes ankylosed with the lumbar vertebrae to form 

 part of the so-called " sacrum." 



2. The number of the prsesacral vertebrae in the different regions 

 of the body is very constantly, if not always, 16 cervical, 5 dorsal, 

 and 3 lumbar. The total number of these vertebrae is therefore 24, 

 or the same as in Man. 



3. The maxillo-palatines vary greatly in form and size, and in the 

 degree to which they are ossified, but they are always lamellar or 

 conchoidal. They unite in the middle line with an ossified septum 

 only in some Cracidce. 



4. There are oval, sessile basipterygoid facets, situated far for- 

 wards upon the rostrum of the sphenoid. 



5. The palatines are long and narrow, with obsolete internal 

 laminae and rounded-off postero-external angles. 



6. The angle of the mandible is produced and recurved, and the 

 oral margins of the rami are not flanged out. 



7. The external xiphoid processes of the sternum (which are 

 much shorter than the internal ones) are bent outwards over the 

 hinder ribs and have expanded ends. 



* Proc. Zool. Soc. 18(i7. p. 41 J. 



