XII ~——- Proceedings of the Association of American Anatomists 
the occipital originated from a common trunk of varying length in the 
three specimens, of which the longest was sixteen centimeters. In one 
specimen the occipital and internal carotid, on the right side, were 
given off as commonly described, but on the left side the internal carotid 
originated five centimeters posterior to the occipital. 
A STUDY OF THE HISTOGENESIS OF THE PIG’S ADRENAL. By R. H. 
WHITEHEAD. Medical Department, University of North Carolina; Hull 
Laboratory of Anatomy, University of Chicago. 
The anlage of the cortex is first detected in embryos about 8 mm. 
long. In passing from older to younger stages this anlage gradually ap- 
proaches the coelomic epithelium, and finally, in the embryo of 8 mm., 
lies in contact with the epithelium immediately lateral to the attach- 
ment of the mesentery. It is very difficult to detect any difference be- 
tween the cells composing the two structures, and the conclusion is 
drawn that the anlage of the cortex is probably derived from the coelomic 
epithelium, either by rapid invagination, or by the wandering of celis 
into the mesenchyme. 
The medulla is first found in embryos of from 30 to 35 nm. At this 
stage it hes spread out as a mantle around the periphery of the cortex. 
The cells composing it are identical in appearance with those which 
compose the adjacent anlagen of the sympathetic gangha; and the mantle 
is in direct continuity with the ganglia by means of connecting strands 
of cells which enter along the dorso-medial aspect of the adrenal, in 
which region the capsule is, in large measure, wanting. Collections of 
cells pass from the mantle in between the cortical rows to reach finally 
their adult position around the central vein in the way described by 
J. M. Flint. 
THE DERIVATION AND SIGNIFICANCE OF CERTAIN SUPERNUMER- 
ARY MUSCLES OF THE PECTORAL REGION. By GeEorGcE S. 
HUNTINGTON. Anatomical Laboratory, Columbia University. 
The primate pectoral region offers peculiar conditions both as regards 
the ontogeny of the pectoral muscles and the development of the ventral 
thoracic wall. As the direct result of these conditions a number of 
anomalous supernumerary muscles are encountered in this region, united 
into a group by their derivation from the muscular sheet of the Pee- 
toralis and by the common etiological factors apparently responsible for 
their production. These variations possess a very definite morpho- 
logical character, and one of the members of the group, the Sternalis, 
occurs in a remarkably constant percentage. The variant muscles are 
