CRANIAL CHARACTKliS OF LACERTA JACKSOM. Z^) 



Occipital Segmexx. — Sapraoccipital. Its epiotic portion is 

 nearly horizontal and only slightly inclines towards the posterior 

 free edge, which forms the vipper margin of the foramen magnum. 

 The processus ascendens (processus spinosus, Clason) rises rather 

 abruptly and almost vertically from the anterior portion of the 

 supraoccipital, and constitutes the exclusive su^'iport of the 

 parietal roof. 



The processus ascendens is not flanked on either side by a.uy 

 apophysial eminence of the supraoccipital, which so frequently 

 acquires the same height as does the spinous process itself, in 

 order to increase the connecting-ai'ea with the parietal, such as is 

 the case in Lacerta oxi/cephala, L.saxicola, L.cleJiUpjyi*^ L. chloro- 

 gaster {boettgeri Meh. ), and L. iiiosorensis^ among some of the flat- 

 headed species ; or as in Lacerta muralis forma typica, the 

 varieties tiliguerta, campestris, nigriventris, &c., as well as Lacerta 

 vivipara, among the more highly and convexly-roofed forms 

 where it also occurs. 



A similar pillar arrangement as pointed out for Lacerta jack- 

 soni is present also in L. simonyi, where it is carried out to 

 even greater perfection owing to the increased elevation of the 

 parietal roof f ; in L. galloti, L. vhHclis, L. diu/esii, and Z. echinata, 

 proportionate, of course, to their respective dimensions of height. 

 This arrangement is of rare occurrence in a strongly depressed, 

 practically platycephalous Lizard, and equally so in the case of 

 the more pronounced pyi'amidocephalous forms, amongst which 

 I find it occurs (in two specimens) in the varieties serpa and 

 lilfordi onl3^ 



The Basioccipital X and Basisphenoid § in no essential deviate 

 in their configuration from the outlines usual in the ^enus for 

 this region. 



The ParaspJienoid is feebly ossified at its base, whereas its 

 centre remains cartilaginous. 



The Orhitosphenoid bones have a broadish appearance on 

 a,ccount of their reduced size, the latter being due to the depressed 

 membranous portion of the ci'anium. 



The 6'qicamosals, usually slender and delicately shaped, which 

 in so many of the smaller forms of iMcerta are only loosely con- 

 nected by ligamentous tissue with the outer postfrontals, are here 

 strongly developed and anteriorly quite fused to the latter. 

 Their posterior ends, which articidate with the quadrates, are 

 broadly expanded and, together with the parietal processes and 

 the much reduced supratempoials which wedge themselves 



* Cfr. Mehelv, " Materialien etc.," Ann. Mus. Nat. Hung., Bd. vii. 1909, tab. xvi. 

 fig. 6, tab. xix. figs. 3 & 10, tab. xxii. fig. 6. 



t Cfr. Siebeurock, 1. c. Taf. ii. fig. 9. 



X Posteriorly and slightly in front of the foramen magnnm there is a small 

 tubercular process in the male specimen, which is absent in the female. 



§ The foramen by which a branch of the jugular vein leaves the skull, and which 

 Siebenrock {I.e. p. 11) regards as the result of synostosis of a special process with 

 the anterior angle above it in the case of the Canary Island Lizards, luit as alisent 

 in the European forms as well as in L. dui/csii, is represented in L.jacksoni by 

 ligament only. 



