412 



Vertebrata. 



•exoccipitals ; the squamosal, in the same region, projects far foi-wards in 

 Snakes, and is connected with the quadi-ate ; the basisphenoid,in front of the 

 basi-occipital, and like this, an ossification in the lower wall of the skull. A 

 parasphenoidisnot developed (c/.. Pish and Amphibia). The anterior wall 

 of the brain-case is often unossified and membranous, sometimes with isolated 

 ossifications. Dorsllly there is a number of bones; the parietals, which are 

 generally (Snakes, Lizards, Oi-ocodiles) fused; the f rentals, an unpaired bone, 

 in Crocodiles and many Lizards; the post-f rentals, behind, the pre- 

 frontals, in front of, and the lachrymals, below, the orbit (the last is 

 present only in Lacertilia and Orocodiha) ; the nasals behind the external 

 nares. Below the oi-bit and behind the maxilla, there is usually a jugal, and 

 from this to the quadrate stretches the q u a d r a t o - j ii g a 1 ; a paired or unpaired 

 vomer lies ventrally, in front of the palatine. Extending from the pterygoid 

 to the maxilla, there is in Ci-ocodiles, Lizards, and Snakes, the peculiar 

 transverse bone which is peculiar to the Reptilia. There is yet another 

 peculiar bone in many Lizards, the columella, extending almost perpen- 

 ■diculai-ly from the parietal to the pterygoid. 



The shoulder girdle of the Reptilia is very like that of the 

 Amphibia. In Lacertilia^ which will he considered first, it is 



'Kg. 337. 



Nirf Ir Tf r,i !iiQf 



Fig. 338. 



Fig. 337. Left half of the skull of a Boa constrictor, seen from the aide (and 

 eomewhat f rom above). — Orig. 



Fig. 338. Do. of a large Crotalus (Orospedoccpfi.aZtis atrox). — Orig. 



Wr frontal, Tn oar bone, Mx maxilla, JTnasal, Os supra-occipital, Fa parietal, FaX palatine, 

 Pe petrosal, P/ postfrontal, Frj prefrontal, Pi pterygoid, Fx premazilla, Q quadrate, Sg 

 squamosal, IV transverse bone, 1, 2, 3 bones of the lower jaw. 



