PHYLOGENY OP THE PAL2EOGNATHJE AND NEOGNATHtE. 195 



surface for the external condyle of the quadrate is cup-shaped. The internal and 

 external angular processes are feebly developed. 



In Rhea the form aud disposition of the articular surfaces agree with those of 

 Dromceus. The internal angular process is large. The symphysis is very broad. The 

 ramus bears a small, perforate posterior lateral vacuity. 



Struthio in the form of its mandible rather closely resembles Dromceus. It differs, 

 however, in its greater relative slenderness, in that it is sigmoidally curved, in the 

 greater relative size of the expanded posterior portion, and in the elongated form of 

 the articular facet for the external condyle of the quadrate. 



JEpyomis also resembles Dromceus. The rami are, however, more laterally com- 

 pressed, have an elongated anterior lateral vacuity, a broad dentary border, and the 

 articular facet for the internal condyle of the quadrate situated at the bottom of a deep 

 cup. The internal angular process is well developed and bears a large pneumatic 

 foramen. 



In Grypturi the mandible resembles that of Rhea. The posterior angular process is, 

 however, longer in Tinamous, and the posterior lateral vacuity appears to be wanting. 



Apteryx differs from all the other forms in the great length of the symphysis, which 

 is about half the length of the ramus. The internal angular process is well developed. 



The coracoid in all the Palseognathine forms is small and rod-shaped. Sometimes, as 

 in Struthio, it is reduced to a mere vestige. The dentary suture is always distinct. 



The Hyoid. 

 Except in Apteryx, only the cera to-branchial s appear to ossify in the Palaeognathine 

 forms. Epibranchials and the true hyoid elements appear to remain permanently 

 cartilaginous. In Apteryx the basihyal appears to ossify at least occasionally. 



The Skull of the Nestling. 



The Cartilage-bones. 

 The youngest of the Palaeognathine skulls in my possession is that of an embryo 

 Dromceus. The cartilage-bones are in all the stages herein described completely 



ossified. 



The basi-occipital, in the young Dromceus mentioned above, is perfectly distinguishable 

 from the neighbouring bones (PI. XLIII. fig. 5). 



It is bounded antero-laterally, and in front, by the basi-temporal plate of the para- 

 sphenoid, and postero-laterally by the exoccipital. It is produced caudad to form 

 the median portion of the occipital condyle. It is interesting to note, however, that 

 it forms only the ventral part of this. It is entirely shut off from the occipital foramen 



