FORMATION OF THE PALATE. 39 
deepen and grow backwards into the roof of the stomatodeum the maxillary pro- 
cesses grow forwards from the lateral boundaries of that space, that is from the 
upper ends of the mandibular arches, and pass beneath the eyes, which now form 
distinct prominences on the sides of the head. The upper borders of the maxillary 
processes come into contact with the lateral nasal processes from which they are 
temporarily separated by grooves, the oculo-nasal sulci. These latter pass from the 
depressions round the eyeballs, the rudimentary conjunctival sacs, to the margins of 
the nasal pits. The anterior extremities of the maxillary processes impinge upon 
the globular processes, and ultimately their upper borders and anterior extremities 
fuse with the lateral nasal and globular processes completing the posterior bound- 
aries of the anterior nasal orifices, and the lateral parts of the primitive upper lp. 
At the same time the oculo-nasal sulci are converted into the lachrymal sacs and the 
nasal ducts, which henceforth constitute the channels of communication between 
the conjunctival sacs and the nose. 
The result of the ingrowth of the maxillary processes and their fusion with the 
lateral nasal and globular processes is the division of the large orifice which led into 
the stomatodeal space into three parts—a large lower, and two smaller upper aper- 
tures. The lower opening is the aperture of the mouth; it is bounded below by the 
Anterior nasal orifice Ethmo-vomerine plate 
sea Nasal cavity 
Eye 
Jacobson’s organ 
Globular process 
Mouth 
Maxillary _ Dental 
process germ 
Labio- 
dental 
Palatal sulcus 
process 
Dental 
germ 
\ 
Pituitary depression Tongue Meckel’s cartilage 
Fie. 31. 
I. Portion of the head of a human embryo about 24 months old (His). The lips are separated from the gums, 
and the line of the common dental germ is visible in the latter. The palatal processes are growing 
inwards from the maxillary processes. 
Il. Transverse section of the head of an embryo after the fusion of the palatal processes of the maxillary pro- 
cesses with the nasal septum, which grows backwards from the fused globular processes. 
united mandibular arches, and above by the fused mesial nasal, and maxillary 
processes. The smaller upper openings are the anterior nares, which on their first 
formation are merely foramina of communication between the exterior and the 
upper part of the stomatodzeal space; the latter is not yet separated into nasal and 
oral chambers. 
Formation of the Palate and the Separation of the Nasal and Buccal 
Cavities.—This separation is effected by the formation of the palate, which is 
developed to a slight extent by the backward growth of the globular processes 
along the roof of the space as a pair of ridges, termed the nasal lamine, which fuse 
together to form a small anterior portion of the palate, viz. the intermaxillary pro- 
cess, in which the intermaxillary parts of the superior maxille are formed. The 
remaining and greater part of the palate is formed by two ledge-like ingrowths, 
one from the inner surface of each maxillary process, which meet and fuse anteriorly 
with the intermaxillary process, and behind this with each other. In these pro- 
jections the palatal processes of the superior maxillze and the horizontal plates of 
the palate bones are formed, and by their fusion the upper part of the stomatodeeal 
space is separated off from the remainder as a common nasal chamber which com- 
municates in front with the exterior by the anterior narial orifices, and behind 
with the pharyngeal portion of the fore-gut by the choanal apertures or posterior 
nares. The lower part of the stomatodzal space and the front part of the fore-gut 
together form the mouth or buccal cavity; this opens anteriorly by a transverse 
