Royal Microscopical Society. 1U5 



The delicate styliform ichthyic maxillaries send backwards the 

 usual jugal style, behind which is the jugal bone (/.), with no 

 separate quadrato-jugal, in these, the highest birds. • The maxillary 

 also sends inwards and backwards the spatulate " maxillo-palatine 

 process " (Fig. 4, mx. p.). 



The long palatines, and the short pterygoids (pa. pg.\ are 

 already well developed, the former sending out its trans-palatine 

 flap of cartilage. The quadrate (q.) has acquired an endosteal 

 patch above, but most of it, like the " articulare " below, is car- 

 tilaginous ; so also is the rest of the mandibular arch ; but four 

 investing bones, viz. the splenial, dentary, surangular, and angular 

 (sp., d., s. ag., ay.), are already far developed. 



I do not see a coronoid in this type. The distinct ends of the 

 Meckelian rods are well seen here, underborne by the two distinct 

 dentaries (Fig. 8, Mh. d.). The only bones in the hyoid arch are 

 the tiny medio-stapedal rod, and the shaft of the lower piece of the 

 " cornu major " of the " os hyoides." 



In about four days later the Thrush's skull shows much to 

 interest the observer (see Plate IX., Turdus merula). All the parts 

 described in the last stage can now be seen more clearly in their 

 fuller development, although very few new centres of bone are to 

 be seen. The most important of these hardened territories is now, 

 however, well shown ; this is the " super-occipital " (s. o.) ; it is 

 a linear vertical patch, affecting the cartilage which lies between the 

 huge anterior semicircular canals (Fig. 7, s. o., a. s. c). This is a 

 true reptilian bone ; and I have seen it single, as yet, in no other 

 bird ; not even in the Kedbreast, Sparrow, or Crow. 



In an unroofed skull (Fig. 6) we see the large prootic (also 

 shown in the last stage — Plate VIII., Fig. Q,pro.); between this main 

 " petrosal " and the ex-occipital is the small " opisthotic " (op.). 

 This figure shows the squamosals at the sides, and the " rostrum " of 

 the parasphenoid projecting in front ; the more solid part of the 

 bone has worked its way into and behind the deep sella turcica (s. t.) : 

 between the end of this bone — now a veritable " basi-sphenoid " — 

 and the basi-occipital, we see the " spheno-occipital synchondrosis." 

 Even in this minute preparation the ali- sphenoid (al. s.) shows its 

 fenestra, and its two foramina (/. ovale and /. rotundum). In the 

 basal region (Fig. 5) the other occipital bones — lateral and basal — 

 are much more developed, and the cochleae (cl.) are well seen in the 

 remaining clear cartilage. 



Farther forwards, the " basi-temporals " (b. t.), and the para- 

 sphenoid (pa. s.) are seen to have acquired increased solidity and 

 ankylosis on the lower surface. An upper view (Fig. 3) shows 

 well the relation of the various parts of the roof, and the gradual 

 advance of the bony territories. The large size of Meckel's car- 

 tilage (Fig. 8, Mk.) is shown by removing the dentary. 



