PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 393 



and I will be obliged to dismiss this cliaracteristic in Opheosaurus here 

 by simply calliug the attention of the student to the fact that, as far as 

 my studies have carried me, it appears that true caudal vertebrse are 

 never reproduced in the new tail, be it only a ijortion or the entire ap- 

 p(mdage is lost, but in their place we have substituted a series of semi- 

 osseous nodules, that eventually form the bony core to the new part. 



The opportunity has not been afforded me to enter very extensively 

 into the occurrence of boue in the exoskeleton of this lizard, but Pro- 

 fessor Owen tells us (Anat. of Verts., vol. i, p. 555) that "bone is devel- 

 oped at the base of the scale, forming part thereof, or combining scute 

 and scale, in Opliisaurus, Tribolonotus, and Trachysaurusy We may add 

 to this that there certainly seems to be more or less bone tissue, be it 

 semi-osseous or otherwise, in the tough and brittle plates that ov^erlie 

 the true skull, superiorly. It requires but a very superficial examina- 

 tion of the skull of this snake-like lizard to satisfy the zootomist that 

 he has before him a creature that, so far as this part of its bony frame- 

 work is concerned, at least, makes a very near approach to the typical 

 Lacertilian, an indication that is more than likely to be carried out in 

 other parts of its anatomy. 



We find the occipital condyle to be uniform in outline, being notched 

 above, with its long axis placed transv^ersely ; it stands out quite prom- 

 inently from the lower margin of the elliptical foramen magnum, which 

 in turn has its long or major axis parallel with the axis of the condyle; 

 prominent though this latter may be, it cannot be said to be peduncu- 

 lated, but really is sessile, its prominence being greatly due to the seg- 

 ments that support it. The part that the basi and exoccipitals took in 

 its formation is plainh" indicated even in the adult by delicate little 

 furrows that mark the boundaries of the original segments. 



This condition of the condyle obtains in many of our American 

 lizards, notably in Gerrhonotus and in Sceloporus and kindred forms 

 among the Iguanidcc. Substantial protection is afforded the brain be- 

 low by the perfect union that has taken place among the bones of the 

 basis cranii, the basisphenoid, basioccipital with the exoccipitals, which 

 latter supjiort tuberous and outstanding paroccipitals. On the other 

 hand, the anterior wall of the brain-case depends solely in the living 

 animal uj)Ou thin membranous partions for the defense of the encephe- 

 lon, the representatives of the ali- and orbitosphenoids. This open 

 space in the articulated cranium is bounded below by the basisphenoid 

 and laterally by the parotic on either side. Above we again find the 

 brain completely guarded by osseous plates, which here are the united 

 parietals, that in turn become indistinguishably amalgamated with the 

 large superoccipital. Mesiad, the united parietals anchylos with the 

 paretics of the brain-case, while anteriorly these bones articulate sutur- 

 ally with the hinder borders of the frontals ; no parietal foramen ever 

 existing at this point as fouiid in some lizards. Laterally, each parietal 

 is extended backwards in a diverging limb, that on either side articu- 



