462 Description of a 4-mm. Human Embryo 
DESCRIPTION OF MODELS. 
MODEL OF BRAIN. 
This model is shown in side view in Fig. 1, and again in Fig. 6, there 
turned so as to be seen nearly from below. The fore brain is divided 
into two parts, one of which includes the anterior neuropore (marked 
by the rolled ectoderm, shown only where that of the brain joins that 
of the skin), the lateral pocket of the optic vesicle, and further from 
the anterior end on the ventral side the enlargement for the hypophysis, 
which fits between the two lobes of this gland arising from the pharynx. 
Fia. 6. Model of brain, seen from below. X 60. 
The relations of the pharyngeal and medullary portions of the hypophysis 
are shown in Fig. 3, the photograph of a section of this part of the 
embryo at this level. Of the other photographs of the brain, Fig. 4 
represents a section of the anterior part of the hypophysis, showing its 
continuity with the cavity of the brain, and Fig. 5, a section passing 
through the optic vesicle and the anterior neuropore. The plane of sec- 
tion is shown by the line between the two pieces of the model. 
In this first portion of the fore brain there are, beside the anterior 
