104 Transactions of the 



and plates, to form secondary sense-chambers outside the main 

 brain-chamber, is well worthy of notice. The bars of the face not 

 only conjugate to form their own basket, they form many and 

 notable connections with the cunning-work of tbe sense-capsules. 



As the cochleae show through the hyaline cartilage below, so 

 also do the elegant " semicircular canals " appear in the hinder 

 view of the skull (Fig. 3) ; and their form would seem to have 

 been for beauty rather than for use ; yet Nature obtains both 

 these ends by one process. The great fontanelle (fo.), or exposed 

 part of the membranous cranium, is still very large ; the roof bones, 

 parietals (p.), and frontals (/.) being scarcely half their proper size. 

 The nasals (n.) have already their characteristic form ; and the thin 

 sickle-shaped squamosals (sq.) are quite like those of a Lizard at 

 this stage. Eeturning to the basal view (Fig. 4), we see that there 

 is a projection answering to the basi-pterygoid (b.pg.), although it 

 is here in these types at its lowest development, and shows scarcely 

 at all in the adult. Farther forwards we see the end of the para- 

 sphenoidal rostrum sheathing the base of the perpendicular ethmoid ; 

 this base being, indeed, formed by the trabecular commissure, and, 

 somewhat higher, by the crest growing upwards from that arch. 

 Already this part is cleft off from the " septum-nasi ": and also between 

 the eyes (Fig. 1, i. o. f.) a "fenestra" has appeared, dividing the 

 trabecular crest below from the ethmo-presphenoidal bar above. 



The optic nerve (2) passes out of a notch between the pre- 

 sphenoid (p. s.) and ali-sphenoid (al. s.) : this latter part is fene- 

 strate, and has below and behind it a foramen (/. ovale, 5) for 

 the trigeminal nerve. The only intrinsic bone in the cranio-facial 

 axis, yet developed, is the basi-occipital; but the parasphenoid (jpa. s.) 

 is grafting itself upon the cartilage bounding the pituitary space, 

 namely, the fore-part of the " investing mass," behind, and the 

 apices of the trabecule around and in front. The nasal septum, 

 like the lateral and median ethmoids, is still altogether cartilaginous ; 

 the lateral ethmoids appear on the top of the head. The alaa- 

 nasi {al. n.) give off huge turbinals (Fig. 4, al. t), and these are 

 separated by the trabecular bar, which is rounded behind, and alate 

 to a large extent in front : it terminates in the spatulate prae-nasal 

 cartilage, the azygous model on which the pras-maxillaries are 

 formed. This rod is becoming absorbed behind, and will soon 

 disappear. 



The ali-nasal cartilage turns inwards behind, and each moiety 

 of the broad-fronted vomer (v.) is grafted upon the corresponding 

 cartilaginous flap ; this is the true " iEgithognathous " structure. 

 I have not seen any " septo-maxillaries " on the angles of the vomer 

 in the Thrushes. The halves of tbe great prae-m axillary are indi- 

 cated by a large notch in front ; the various processes, nasal, marginal, 

 and palatine, are all well developed. 



