38 GENERAL EMBRYOLOGY. 
Whilst the boundaries of the stomatodeal space are being defined, two oval 
depressions, lined with thickened epithelium, appear in its upper boundary on the 
lower and anterior surfaces of the fronto-nasal process; these are the olfactory pits 
or depressions. A portion of the epithelium of their walls is separated off and takes 
part in the formation of the olfactory bulbs, whilst the remainder is transformed 
into the olfactory epithelium, from which the olfactory nerve-fibres grow inwards 
to the olfactory bulbs. As the olfactory pits deepen they grow backwards into the 
roof of the stomatodeal space, and at the same time they separate the lower portion 
Cerebral hemispheres 
tas 
Olfactory pit 
Globular process 
Maxillary process Olfactory pie 
itui Maxillary process 
Pituitary {axillary process 
depression 
Globular process 
Trachea 
Cerebral 
hemisphere 
Nasal cavity 
a acobson’s organ 
Ant. nasal orifice ses = 
Globular process Globul 
' obular process 
Maxillary process 
: Maxillary process 
Lower jaw 
Lower jaw 
Mouth 
Fia. 30. 
I. Portion of the head and neck of a human embryo 32 days old. The floor of the mouth and pharynx and 
the ventral part of the anterior portion of the body have been removed. By the approximation of the 
globular and maxillary processes the boundaries of the anterior nares are almost complete, but the 
olfactory pits still open in the whole of their lengths into the roof of the mouth (from His). 
II. Transverse section of the head of an embryo, showing the close apposition of the globular and maxillary 
processes. 
III. Head of human embryo about 2 months old, showing the union of the globular processes and their fusion 
with the maxillary processes. The anterior nasal apertures are now completely defined (from His). 
IV. Transverse section of the head of an embryo, showing the fusion of the mavyillary processes with the 
globular processes, and the separation anteriorly of the nose from the mouth. 
of the fronto-nasal process into three parts, constituting a median and two lateral 
nasal processes. At each lateral angle of the median nasal process a spheroidal 
elevation, the globular process, appears. The part of the median nasal process 
which intervenes between the two globular processes is divided into two areas, an 
upper triangular and a lower quadrilateral, by the appearance of a tranverse ridge, 
which is afterwards moulded into the tip of the nose. The upper triangular area 
becomes the dorsum of the nose, and the lower quadrilateral area forms the 
columella, z.e. the lower and anterior part of the septum between the anterior 
nasal apertures. The globular processes are utilised in the formation of the philtrum 
or middle part of the upper lip, and the lateral nasal processes form the ale of 
the nose or lateral boundaries of the anterior nasal apertures. As the olfactory pits 
