106 Transactions of the 



The " oshyoides " has still the single bone on each side, behind. 

 The extreme beauty of the auditory labyrinth is displayed in the 

 outspread occipital cartilage (Fig. 7), which contains much of the 

 structure of the inner ear. The rest of the figures of this stage 

 will speak for themselves, as mere advances upon the last stage. 



In nestlings of Turdus merula a week old, the elegance of the 

 sylvine type of skull becomes more manifest (Plate X.) ; taking 

 figure by figure, we shall observe how the advance is all in the 

 direction from a somewhat generalized to an extremely specialized 

 form of skull. On the side (Fig. 1) we see the skull-roof is much 

 more complete, the beak becoming more ossified and slender, and 

 an osseous centre in the perpendicular ethmoid (p. e.), outside of 

 which is the large " pars-plana " (p. p.). The ali-sphenoid (al. s.) 

 is largely ossified, and also the quadrate (</.), and below this the 

 articulare (ar.) is now bony. Below (Fig. 2), besides the extension 

 of the bony matter, we have the more typical form of the various parts, 

 everything becoming more and more slender and elegant, as is the 

 wont in these soft-billed singing types. Especially we may note 

 the more out-curved and enlarged extremities of the maxillo-palatine 

 hooks, and the finer shape of the parasphenoidal rostrum. 



In the upper and hinder views (Figs. 3 and 4) we find that 

 the azygous super-occipital (s. o.), which has now grown on to the 

 arch of each anterior semicircular canal. 



The sectional view (Fig. 5) shows the cranio-facial cleft (c. f. c.) 

 between the septum-nasi and the fast-ossifying perpendicular 

 ethmoid (p. e.) : the rest of the interorbital septum is soft. The 

 position of the vomer (v.), with regard to the parasphenoid (pa. s. ), 

 is shown ; and the latter bone has grown far up into the sella 

 turcica, and has coalesced with the basi-temporal (b. t.). The 

 fenestrate ali-sphenoid (al. s.) has on its supero-posterior angle the 

 square inner face of the large squamosal (sq.), and behind this and 

 the oblong parietal {p.) is the huge "prootic" (pro.); behind 

 which is the small opisthotic wedge (op.) ; which in turn is followed 

 by the ex-occipital (e. o.). The prootic, basi-occipital, and basi- 

 spheuoid, together form a triradrate suture. I have not been able 

 to find either an " epiotic " or a " pterotic " in these birds. The 

 inner face of the mandible (Fig. 5) shows no " coronoid " ; the 

 median part of the " os hyoides " (Fig. 6) has a basi-hyal, and a 

 " uro-hyal " bone ; and the upper shaft has been developed on the 

 large cornu (Or. 1). 



In the growing and adult birds I have studied Turdus merula, 

 musicus, viscivorus, pilaris, and iliacus ; the skull differs from that 

 of the Crow in elegance as well as in size ; and the bony tissue 

 is extremely light and delicate. The bony " siphonium " is as large 

 relatively ; but the smaller additional bones are fewer and lesser. 

 The septum-nasi does not ossify, nor any of the nasal cartilages 



