572 EDWARD PHELPS ALLIS, JR. 
the neurocranium and its insertion on the ventral surface of the 
anterior portion of the vertebral column. 
The antero-mesial edge of the muscle-sheet is practically paral- 
lel with the pharyngobranchials, and at once suggests that a 
pharyngohyal must primarily have existed there. There are, 
however, no special tissues that seem to represent rudiments of 
that element. Attached to the interarcual ligament which gives 
origin to this part of the muscle, near its anterior end, there was, 
in one specimen, a small and delicate piece of cartilage, which 
is apparently one of the interarcual cartilages, to be later de- 
scribed, and not a rudimentary pharyngohyal. 
The efferent branchial arteries, in all three specimens, perfor- 
ated the median subaortal membrane and ran antero-laterally 
across the ventral surface of the muscle-sheet to its lateral edge, 
each artery reaching the edge immediately anterior to the 
pharyngobranchial of the arch to which it belonged and slightly 
mesial to the distal end of that pharyngobranchial. The artery 
then ran outward across the anterior edge of the pharyngo- 
branchial, crossed the dorsal (external) surface of that cartilage 
and so, having passed dorsal (external) to the related dorsal 
interarcual ligament, reached the external surface of the 
epibranchial of its arch. The vena jugularis lay everywhere 
dorsal to the sheet of muscular and ligamentous tissues and hence 
dorsal also to the pharyngobranchials. 
The pharyngobranchials of Chlamydoselachus see lie in a 
sheet of muscular and ligamentous tissues which, although it 
lies immediately internal (dorsal) to the lining membrane of the 
branchial chamber, is separated from that lining membrane by 
the efferent branchial arteries. The latter arteries therefore lie, 
in a part of their course, ventral (internal) to the pharyngobran- 
chials, and as these latter cartilages are universally considered 
to lie primarily internal to the arteries it seems quite certain 
that, in Chlamydoselachus, the dorso-mesial ends of the pharyn- 
gobranchials became secondarily attached to the muscle-sheet, 
which primarily lay dorsal to them as well as to the efferent 
branchial arteries, and were in consequence lifted upward dorsal 
. both to the latter arteries and to the dorsal aorta. If this 
