300 Herr F. Siebenrock on the 



serves for tlie rccc]jtion of the olfactory nerves, and consists 

 in Ilatteria of tough cartiLiginous tissue, while in the majority 

 ot lizards it merely remains in a membranous condition. 



II. 



The bony cranium consists, as in all lizards, of the occipital 

 and sphenoid groups of bones. The latter \sic\ — former?], 

 again, is composed of the basioccipital, supraoccipital, and the 

 two pleuroccipitals which lie between these. All four 

 occij)itals enclose the occipital foramen, an oval aperture with 

 a greater vertical than transverse diameter, on the lower 

 circumference of which the unusually large occipital condyle 

 is developed as a semilunar tubercle. In Hatteria this is 

 formed in a conspicuous degree from the basioccipital, wdiile 

 the two pleuroccipitals take a much smaller share in it, in 

 contrary iashion therefore to what we find in the chama^leons, 

 in which the partes condyloidcffi of the pleuroccipitals are 

 much larger than tlie pars condyloidea of the basioccipital. 

 In adult individuals the four occipital elements are indistin- 

 guishably fused together, while in specimens which are still 

 young they remain separated by sutures, precisely as in the 

 case of the rest of the Laccrtilia. Now in young specimens 

 we fird that the pleuroccipital is composed of two bones, 

 which are separated one from another by a suture. The one 

 bone with its ])ars condyloidea is connected in the shape of a 

 semicircle with the basioccipital below, constitutes the lateral 

 margin of the occipital foramen, and unites above with the 

 supraoccipital. From the middle of its external circum- 

 ference a short pointed process projects almost horizontally 

 outwards. This bone is manifestly, according to position 

 and function, the pleuroccipital — exoccipital of Owen and 

 Huxley. Before this there lies a bone, which unites with the 

 otos))henoid in front, with the supraoccipital above, and with 

 the basioccipital below. Its posterior surface is convex and 

 its anterior concave, with which it forms the posterior wall of 

 the bony labyrinth. The processus paroticus projects out- 

 wards and backwards. I consider this bone as the parocci- 

 pital, exoccipilal of Briihl, and opisthotic of English authors. 

 Giinther also describes {loc. cit.) a paroccijntal, which, how- 

 ever, caimot be quite identical with that discovered by me. 

 According to this author the paroccipital is superimposed 

 upon the jnoccssus i)aroticus merely in order to strengthen it, 

 without taking part in the formation of tlie auditory appa- 

 ratus. Giintiier writes : — " Jt [namely the processus paro- 

 ticus] is strengthened by a paroccipital, which covers nearly 



