223 
Royal Microscopical Society. 
From the stored-np wealth of the egg tilings new and old have 
been required, and an architectural process has freely applied the 
lime which was ready at hand. This hardening of the walls has 
given us new bony centres, and has obliterated the distinction be- 
tween others that were separate. Turning to the basal view, we 
see that the minute bone-sheath of the notochord has become a re- 
cognizable “ basi-occipital ” (Plate XXXVI., Fig. 1, b. o.) ; the “ basi- 
temporals” (b. t.) have become one broad unbent-bow- shaped piece, 
and the parasphenoid, or “ sphenoidal rostrum ” (r. bs.), has got its 
ichthyic “ temporal wings,” has grafted itself upon the skull-base, 
and is being fused with the basi-temporal. The lateral occipital 
region has now its proper ossifications, the ex-occipitals (e. o.) ; and 
the upper part of the arch has begun to ossify by another pair of 
centres, the supra-occipitals (Plate XXXVI., Figs. 4 and 5, s. o.). 
On the roof (Fig. 3, p.f.), the parietals and frontals meet at the 
mid-line, and the nasals (n.) and prae-maxillaries (p. x.) have begun 
to acquire their permanent form. In the side view (Fig. 2), the 
squamosal ( sq .) is seen flanking the roof-bones ; *the ali-sphenoid 
( al . s .) has a bilobate osseoiis centre, evidently by the fusion of two 
smaller ones. Attached to the large “ ecto-ethmoidal ” flap, or 
“ pars plana ” ( p. p.), is a small rod-shaped lachrymal (l.) ; in this 
side view also the fish-like character of the maxillary ( mx .) is well 
seen, as also the ectosteal patch on the quadrate ( q .). Below, the 
ptery go-palatine arcade (Fig. 1, pg. pa.) has developed greatly, and 
the free cartilaginous “ trans-palatine ” flap has become typical in 
form. The mandible (Fig. 2, outer view ; and Plate XXXV., 
Fig. 7, inner view) is now in a characteristic reptilian condition, 
with its one endosteal bone and its five parosteal investments. In 
the hyoid arch the shaft of the stapes (Fig. 2, st.), and the proximal 
pier of the “cornu major ” (Fig. 6, br. 1), have each acquired an 
ectosteal sheath. The small cerato-hyals {c. hi), the “ basi-uro-hyal” 
(b. h., u. hi), as well as the distal part of the long rod (third post- 
oral), are still mere cartilage. 
A longitudinal section (Plate XXXV., Fig. 7) shows much that 
is instructive. The exact relation of the roof-bones to the cranio- 
facial axis ; the large ear-capsule, with its prootic {pro.) and opis- 
thotic ossifications {op .) — the only centres I have found in this 
type ; and the notch and fenestra that re-differentiate the trabeculae. 
The “interorbital fenestra” {i, o. s.) is suboval, and somewhat 
tilted backwards. The cranio-facial cleft {c. f. c.) has severed the 
thick trabecular bar and its crest, and is creeping upwards so as to 
divide the ethmoid (eth.) from the nasal septem {s. n. ). The vome- 
rine moiety (v.) is seen beneath the hinder half of this notch ; and 
beneath it the palatine {pa.). The “ rostrum,” or parasphenoid, 
nearly touches the basi-temporal (b. t.) ; and partly ossifying the 
“ sella turceca,” has behind it the “ spheno-occipital synchondrosis.” 
VOL. vm. s 
