DEVELOPMENT OF THE SKULL IN THE CROCODILIA. 291 
the figure the hinder part of the soft palate is cut away so as to expose the “‘ posterior 
nares” (i.2), which open into a circular recess. Behind them there is a smaller 
notched fold of membrane, and over the notch a round median passage; this is the 
middle Eustachian passage (m.ew), it opens into the basis cranii. 
At a short distance outside this there is, on each side, a curved valvular opening ; the 
broader end of each is behind, and these ends approximate; the convex edge of each is 
postero-lateral; these paired openings are the lateral Eustachian openings (/.ew), and 
run directly into the main tympanic cavity. 
7th Stage. Nearly ripe, and ripe embryos of Crocodilus palustris, taken from September 
4th to September 8th, total length 10 to 103 inches; and ripe embryos of Crocodilus 
1, sp. 
a. Endocranium. 
The general form of the parts of the endocranium alters but little during the last 
month—August 8th to September 8th; its changes are mainly increase of size and 
consolidation of the various regions, especially the bony centres. ‘The two paired and 
the two unpaired bony tracts of the occipital arch (Pl. LXIX. figs. 7, 8, ¢.0, s.0, 6.0) 
now form a strong ring of bone, with very limited synchondroses dividing its elements. 
The basioccipital (b.0) does not reach the basisphenoid (d.s), nor fill all the cartilage 
belonging to it behind; thus the condyle (oc.c) is a solid mass of cartilage, and not a 
mere articular plastering left on the bone. The form of the bone is roughly pentagonal 
(Pl. LXX. figs. 1 & 3, 6.0), and it is separated from the other bones by narrow tracts 
of cartilage. It is somewhat grooved in the middle, below, and mamillate right and 
left, and its gradually narrowing hinder part is imbedded in the reniform condyle, 
whose “ hilus” is filled with the remnant of the notochord (v.c). A common round 
opening leads into both this bone and the basisphenoid, for one pneumatic cavity 
occupies both; the opening is the ‘‘ middle Eustachian passage” (m.ew). In the front 
of each lateral angle there is another, lesser passage, which is the posterior opening ot 
the “lateral Eustachian tube” or passage (/.ew). This opens into a lateral chink behind 
the basitemporal plate (0.t) (Pl. LXX. figs. 3, 4, & 8, /.ew), and this chink leads also 
into the excavated basisphenoid, the anterior opening of the “lateral Eustachian tube.” 
The large, winged exoccipitals (¢.0) and their synchondrosial cartilages complete the 
ring over the foramen magnum (Pl. LXIX. fig. 11, and Pl. LXX. figs. 1 & 3, fim). 
They are large, irregular, multangular shells of bone—shells both in their general 
convexo-concave form, and also because they are hollow or pneumatic. They are 
riddled with holes on their lower surface, but each hole has its meaning and function. 
The hindermost of these, nearest the condyle, is for the hypoglossal nerve (x11), then 
there is a small passage for a vein, and outside in front of that a hollow with two 
passages, these are for the vagus and glosso-pharyngeal nerve (X, 1x). At the antero- 
internal angle there is a notable round hole; this leads to a more or less perfect bony 
