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, 



