396 
MR. W. K. PARKER ON THE STRUCTURE AND DEVELOPMENT 
between it and the maxillopalatine bar part of the first cleft ( l.cl .) is clearly seen 
towards tlie “inner can thus.” 
Above and behind the junction of the maxillopalatine and mandibular regions, 
therefore above and behind the angle of the mouth at this stage, we see the form of 
the ear-capsule, whose cutaneous investment is very thin, above. Behind the angle of 
the jaw, and below the ear -ball, the first post-oral cleft is still visible, and behind 
it the other three, the hyo-branchial and branchial clefts, are still evident as chinks fast 
closing in (figs. 1, 2, cl. 1-4). 
It will be seen that the angle of the lower jaw (figs. 1, 2, ran., mk.) has already 
gained a position so far backwards as to be directly beneath the involution of the ear- 
sac ; it looks now directly backwards. In the last stage this angle was placed between 
the eye and ear, and looked forwards and upwards (Plate 27, fig. 3, ran.). 
So rapidly has the face taken on that peculiar metamorphosis which results in the 
formation of the adult Snake’s mouth — a mouth which opens behind the head, at a 
distance equal to half the length of the head (Plate 32, figs. 1 and 2). 
The immense eye-balls are acquiring sockets, the membrano-cranium. adapting itself 
to their form ; but they are too independent of the skull to need more than a casual 
notice here. 
The ear-balls, on the contrary, are becoming part of the skull ; they are chonclrified 
now, and much elongated (figs. 6-8). 
In the younger embryo (fig. 6) we see the auditory capsules marked off from the 
investing mass (iv. ) by younger cells ; they reach from the glossopharyngeal nerve 
(9) to opposite the entrance of the internal carotid arteries (i.c.). 
Between the capsules and the narrow anterior part of the investing mass there is 
a large rounded notch ; over this membranous space the Gasserian and facial ganglia lie. 
The space between the notch and the hind margin shows two important structures 
below ; the first of these is a small pouch containing otoconial granules : this is the 
first appearance of the cochlea (cl.) — first, practically, in the Vertebrata, as well as in 
the individual embryo. 
Behind this ingrowing pouch there is an opening, and to the membrane stretched 
across this opening the small hyoid cartilage is attached : the membranous space is the 
fenestra ovalis ; the liyoidean rudiment will be the columella (figs. 6, 7, hy.). 
Partly occluding the notch in front of the cochlea is an ear-shaped flap of cartilage, 
widest behind, and having its crescentic or concave edge looking outwards ; this is the 
small infero-lateral alisphenoid ( al.s .). 
In front of the optic nerve in the older embryo (fig. 8), a patch of thickening tissue 
shows the rudiment of a similarly independent orbito-sphenoid (o.s.); the independence 
of these tracts is characteristic of the Ophidia ; as yet I have seen no other instance. 
Looking now at the side view of the ear-capsule in the younger embryo (fig. 7), we 
see that the two post-oral cartilages lie on its side ; the second is attached, the first lies 
loosely against it : the meaning of this will soon be apparent. 
