332 The Alligator and Its Allies 
small, oval mass of very fine tubules (&), which do 
not stain so darkly as do the Wolffian tubules; 
this mass is apparently the beginning of the 
permanent kidney, the metanephros. Its tubules, 
though their origin has not been determined, seem 
to be entirely distinct from the tubules of the 
Wolffian body. 
A single vertical section through the anterior 
part of the head of an embryo of this age has been 
represented in Figure 23b. On the right side the 
plane of the section cut through the lens of the eye 
(In); on the left side the section was anterior to 
the lens. The upper (wl) and lower (Jl) eyelids 
are more evident here than in the surface view. 
Owing to the hardness of the lens, its supporting 
structures were torn away in sectioning. The 
vitreous humor is not represented in the figure. 
The superior (ur) and inferior (Jr) recti muscles are 
well shown on the right side; they are attached to 
the median part of a Y-shaped mass of cartilage (se), 
which may be termed the sphenethmoidal cartilage. 
Between the branches of this Y-shaped cartilage the 
anterior ends of the cerebral hemispheres (ch)— 
better called, perhaps, the olfactory lobes—are 
seen. Between the lower end of the spheneth- 
moidal cartilage and a dorsally evaginated part of 
the pharynx are two small openings (pm); when 
traced forward these tubes are found to open into 
the convoluted nasal chamber, while a short dis- 
tance posterior to the plane of this figure they unite 
