4a Ae Fietp CoLtumBian MustumM—GEo ocy, VOL. II. 
in a median symphysis for a short distance back of this interclavic- 
ular foramen. The under or convex surface appears only for a small 
space between the ends of the scapule, epicoracoid processes and the 
episternum. Its outer extremity extends into a slender process, 
broken away in the specimen figured, which reaches alohg the front 
margin of the ventral ramus of the scapula to the base of the dorsal 
ramus. (See Pl eles 
The clavicle seems to be the most variable bone in the skeleton ; 
I know of no form in which it is better developed. In Cryptocldus it is 
a small, triangular bone, meeting its mate in the middle line, according 
to Andrews, the episternum being absent. In Plesvosaurus mudget 
Cragin (see Pl. XXVII), the clavicle appears to have been smaller 
and more triangular than in the present species. It is generally 
assumed that this bone is the real clavicle by Seeley, Andrews, Fiir- 
bringer and others, and one may, with Andrews, explain its position 
in relation to the ventral ramus of the scapula by the peculiar method 
of ossification of that bone. But, can its visceral relations to the 
coracoid and episternum be explained as easily? It is true that many 
authors call the median, un- 
paired piece the interclavi- 
cle, a membrane bone, and, 
if this origin 1s accepted, its 
position in relation to the 
clavicle is not.remarkable. 
But I am inclined, with Geg- 
enbaur and Fiirbringer, to 
believe that this central piece 
is really the episternum, a 
cartilage bone. Andrews 
described the clavicle in some 
forms as showing a sutural 
tendency with the scapula, 
and in some forms, as ///as- 
mosaurus, it seems to become 
entirely fused with that bone, 
or if not, has disappeared 
entirely. 
FIG. 9. The cpisternum  (inter- 
Episternum. of 7yinacromerum anonymum Will. 
one-half natural size. 

clavicle) is a small, symmet- 
rical bone deeply emargi- 
nate in front and behind. The thin squamous margin on each 
side underlaps the clavicle. These squamous borders seem to have 
