POISON APPARATUS OF VENOMOUS SNAKES 65 
Among the bones indirectly concerned the ectopterygoid bone and the pre- 
frontal bone are the most important. ‘The ectopterygoid is connected with 
the maxilla by a broad, strong horizontal ligament at the lower border of the 
posterior surface of the maxilla, and at its hind end is attached firmly to the 
upper surface of the endopterygoidal bone near the middle part of the latter. 
The prefrontal bone is connected with the articulating, small, ovoid surface of 
the upper corner of the posterior surface of the maxilla. This joint is mobile. 
The articulation of the prefrontal with the frontal bone admits a certain 
amount of movement. Thus there are two points on the posterior surface 
of the maxilla, one at the upper and one at the lower end. Should the ecto- 
pterygoid be brought forward by certain muscular movements, it would 
necessarily result in rotating the maxilla at the maxillo-prefrontal joint and 
force the maxilla with its fangs to project in a forward direction; hence the 
erection of the fangs. 
The endopterygoid bone is two-thirds anterior straight and one-third pos- 
terior slightly turned upwards. In the anterior end it is jointed with the 
palatal bone, which is short and vertically flattened. The posterior end is 
loosely connected with the mandibulo-quadrate joint. The ectopterygoid is, 
as stated above, firmly ankylosed at the upper surface of the middle way of 
the endopterygoid. The latter has several teeth (solid) under the surface. 
Just behind the prefrontal bone (paired) is the frontal bone (paired), and 
behind the latter the parietal bone (unpaired, but fused at the median line). 
The frontal bone is slightly depressed in the upper surface (practically a flat 
roof) and of square shape. On the internal margin it joints with the cor- 
responding part of the other frontal; in the frontal edge it is free, but forms 
a posterior wall of the nasal cavity. Below it has a large foramen for the 
olfactory nerve. The premaxillary bone is connected with the median 
frontal fusion line of two frontal bones by a tiny projection. The lateral 
edge of the frontal is a slight curve which forms the upper edge of the orbit. 
Here the bone is very thin and shows the tendency of a vault underneath. 
At the posterior edge the frontal is jointed with the parietal bone. The 
parietal bone has a lateral process on each side, near the articulation with the 
frontal—the posterior orbital process—which forms the posterior upper edge 
of the orbit. The process leads inwardly to a transverse crest. On the under 
surface, near the median line, on each side, there is an oval foramen which 
communicates with the cranial cavity, and which is the optic-nerve path. 
The parietal bone occupies the largest dimension of the cranium and incloses 
in it an irregular, oblong cavity for the reception of cerebral and cerebellar 
contents. On the upper surface it is flat, but on the under surface the median 
line develops into a sharp, triangular crest enormously elongated, especially 
toward the posterior part (sphenoidal crest), into a projection. The tem- 
poral bones seem to be completely fused with the posterior part of the 
parietal, and three holes (two larger and one small; the two large ones become 
one inside) are found near the posterior edge (lateral and inferior surface) 
of the parietal. Just above them, namely, on the posterior upper surface, 
