226 
up to some distance, so that the length of the sternal forman to 
can now also be indicated with respect to the ribs. In caudal 
direction the sternum reaches to the level of the third rib. Between 
the sternal formation and the ventral ends of the ribs we find every- 
where loose mesenchyme. 
. 
err 
Fig. 3. Lacerta agilis I. transversal. 
In the embryo Lacerta agilis K (N.T. about 29), which is only 
slightly older than the preceding one, again a clear partition of 
coracoideum and sternum is present, a fact which strikes one also 
in studying the embryo Lacerta ag. G., which represents the same 
stage of development as the embryo K. The zone of partition, bere 
again present, is nothing else than the formation of the later sterno- 
coracoidal articular cavity. Both the embryos G and K have a paired 
sternal formation, reaching caudally to the level of the third rib, 
and separated from the ribs by loose mesenchyme. 
In the embryo Lac. agilis H (N.T. about 30) a considerable progress 
is noticed. This progress concerns the form of the parts of the skeleton 
as well as the histological differentiation. In the vertebral arches we 
find cartilage, round the cartilaginous humeral diaphysis we find a 
thin coat of perichondral bone. Diagram 4 brings us one half of a 
transversal section in which the ventral end of the first thoracic rib 
(the first future vertebro-sternal rib) is found. The purpose of the 
