No. 408.] STUDY OF MAMMALIAN EMBRYOLOGY. 917 
sinus (C..S.), and to the disappearance of the second to fourth 
gill-clefts. The neck-bend is so great that the mandibular 
and nasal regions of the embryo are closely appressed to the 
cardiac region of the body proper. The cephalic region has a 
second flexure, the head-bend proper, which marks the site of 
the mid-brain, and in the figure appears as a rounded angle 
obliquely above the eye. From the mid-brain one axis, hori- 
Ven. Md. Au. 
Fic. r, — Pig embryo of romm. A.Z., anterior limb; 4., auditory, or first, gill-cleft; C.S., 
cervical sinus; Z7.L., hind limb; Md., mandibular process; M.L., milk-line ; Mx., maxil- 
lary process; W., nasal pit; Of., eye; Seg., muscular segment ; Um., umbilical cord; 
Ven., floor of fourth ventricle (medulla oblongata). x 8 diams. 
zontal in the figure, extends backward through the region of 
the fourth ventricle, or hind-brain (Ven.), to the neck-bend, 
while the other axis extends vertically downwards to the region 
of the fore-brain, which is marked by a rounded protuberance 
in the outline of the head. The dorsal outline of the body 
proper forms a long sweeping curve, ending in the tail; this 
dorsal. curvature is another characteristic of the amniote 
embryo, the back in the embryo of fish-like forms being 
