Royal Microscopical Society. 7 



cartilage walls, in the tympanic cavity ( ty.). On the side of the 

 notochord, and in front of the vagus nerve passages the rudimen- 

 tary cochlea are seen (cl) lying imbedded, as in a burrow, in the 

 substance of the basilar plate. 



In front of these cavities the cartilage is still of great width, its 

 outer edges bounding the drum-cavity, anteriorly. Much of the 

 cartilage in this " basi-temporal " region is undergirt with a pair of 

 bony rafters, that have become slightly fused together at their fore- 

 end ; these are the " basi-temporals " (b. t.). When these are removed 

 (Fig. 3), we find the cartilage deficient at the mid-line ; this space, 

 which becomes very large, and is a great chink in the nestling, is the 

 " posterior basi-cranial fontanelle " (p. b.f.) of Kathke ; the " invest- 

 ing mass-" meets in front of it, and in front of that commissure we 

 have the space lying between the out-bowed apices of the trabeculae 

 — the "pituitary space" (py.). This space is floored with carti- 

 lage in Sharks, Frogs, and Mammals, and that floor is the seat of 

 the " turkish saddle " (sella turcica) of the human skull. In the 

 Bird, as in the Osseous Fish, this saddle has no cartilaginous seat, that 

 is formed below, by secondary bony matter, the " parasphenoid." 

 On each side of the " anterior basi-cranial fontanelle," or " pitui- 

 tary space," we see projections of the much-narrowed cartilaginous 

 mass ; these are the tops of the " first prae-oral facial arch," or 

 " trabeculae cranii "; they have coalesced by their inner margin 

 with the terminal part of the "investing mass"; the face is there 

 grafted upon the skull, and from this point, the middle of the 

 " basi-sphenoidal " region, the cranial cavity is up-tilted, its fore- 

 part resting on the wall-plate of the great interorbital partition. 

 Eapidly the trabecular bars run inwards, meeting each other at the 

 mid-line, and becoming welded together in a long commissure to their 

 very end. Hence, at this part, below the partition- wall of the eye- 

 sockets, the basi-facial bar — it is no longer basi-cranial — is a rounded 

 mass of cartilage with an ascending keel ; it is a plank of cartilage 

 strongly beaded below and set edgewise with the "bead" down- 

 wards. But this interorbital wall is underbuilt by another kind of 

 material, as though a beam of soft wood should be strengthened by 

 clamping along it a narrow, grooved plate of metal. In so small a 

 creature as this germ of a Titmouse I found a good object for the 

 examination of the tissues that compose this part of the face. So 

 much of the "interorbital" wall as belongs to the trabeculae is 

 shown in Fig. 7 ; it was prepared by caustic soda and glycerine, 

 and examined by an inch-focus lens with the lowest eye-piece. The 

 middle of the upper part (*. o.f.) was found, like the ** perichondrium " 

 which had been removed, wholly of connective-tissue fibres, — long, 

 delicate spindles. Down to near the base was all hyaline cartilage ; 

 then a tract of soft, much younger cells, — indifferent tissue ; and 

 then a form of tissue intermediate between hyaline cartilage and 



