No. 408.] STUDY OF MAMMALIAN EMBRYOLOGY. 925 
Fig. 5 is from section 321, and is therefore considerably 
lower down in the series than the section represented in 
12.0 . Nose Dran Ao.4, fourth aortic arch; Az., 
ctodermal depression of the first or auditory gill-cleft; Cerv.z, first cervical nerve; ` 
i ical nerve ; d. lion nodosum (lower vagus 
m 
sverse section 321. 
nerv' 
. rve; OLJI ramus externus 
accessorii; S.C., spinal cord; Thy: Ve. vein; iii, 
third gill-cleft of the right side. x 22 
It passes through the cervical sinus a 
and therefore also through the spinal 
s two distinct unequal parts: 
Fig. 4. nd olfactory pits 
(compare Fig. 1), cord of 
the neck. The section comprise 
