SKULL. 359 



bones and posteriorly with the highly mobile quadrates. (7) 

 There is no parietal foramen. (8) The rami of the lower jaw are 

 not united at the symphysis but connected only by an elastic 

 ligament. 



Tlie supraoccipital does not enter into the foramen magnum 

 (Fig. 197-4, Osp). The parietal is unpaired and sends down 

 lateral processes which articulate with the basisphenoid. The 

 frontals are paired and send down lateral processes which unite 

 with one another on the floor of the skull dorsal to the basi- 

 sphenoidal rostrum. This is a unique arrangement. 



Whether these downward processes contain elements of the orbito- 

 sphenoid and ahsphenoid is not clear. According to Rathke * the parietals 

 and frontals arise from paired centres of ossification in patches of cartilage 

 in the dorso-lateral part of the skull. That there is something imusual 

 in this part of the skull is further rendered probable by the fact that the 

 trabeculae cranii persist in many adult snakes as two separate cartilaginous 

 rods placed in grooves on the dorsal side of the basisphenoidal rostrum 

 and ventral to the union of the frontals. 



There are postfrontals behind the orbit, and prefrontals lying 

 upon the ethmoid cartilage in front of the orbit (Fig. 197 A, F', Pf). 

 The prefrontals have descending processes for articulation with 

 the maxillae and palatines. There are two nasals and two 

 vomers (vo) close together and in front of the choanae {Ch). 

 The quadi'ates are very moveably articulated to the posterior 

 end of the squamosals, which are elongated and project back 

 from the parietal region of the skull (Fig. 197, Qu). 



The lower jaw contains the usual bones but the coronoid is 

 sometimes absent. The hyoid is much reduced, consisting of a 

 pair of cartilaginous rods lying ventral to the trachea and 

 united in front. 



In the Typhlopidae the palatines are placed transversely and meet in 

 the middle line. The pterygoids are not joined to the quadrates and there 

 is no transpalatine. In Xenopeltis, which like Python has teeth in the 

 premaxilla, the squamosal is applied to the side wall of the skull, so that the 

 short quadrate appears to articulate directly with the slcull. In most 

 non-poisonous snakes a row of recurved teeth is present on the maxillae, 

 palatines and pterygoids, the palatine and pterygoid are arranged longi- 

 tudinally and are firmly connected, and the squamosals are slightly move- 

 able. In the Viperidae the maxillae are short and moveably articulated 

 with the prefrontal. The squamosal, and quadrate are very moveable 

 and the pterygoid is moveably attached to the palatine. The maxillae 

 each possess only one large tooth — the poison fang — which contains a 



* Veb. d.[Enttff{ckelungsgesch. der Natter, Konisberg, 1839. 



