250 



ZOOLOGY 



SECT. 



leading into the cavity of the auditory capsule containing the 

 membranous labyrinth. 



In front of the auditory capsules a considerable part of the 

 cranial wall is formed of cartilage, and presents above a single 

 large and a pair of small fontanelles (Fig. 870, fon. fon') but 

 anteriorly it is ossified by the sphen-ethmoid, or girdle-lone 

 (SP. ETH), a short bony tube divided by a transverse partition 

 into an anterior compartment which lodges the hinder ends of 

 the olfactory sacs, and a posterior compartment which contains 

 the olfactory lobes. The anterior compartment is again divided 

 by a vertical partition which separates the olfactory sacs from one 



EX.OC 



M.MCK 



SQ 



-PTG 



EX.OC 



FIG. 871. Rana temporaria. The skull. A, from beneath, with the membrane bones re- 

 moved 011 the right side (left of figure); B, from the left side, with mandible and hyoid ; 

 C, from behind, a. c. hy. anterior coniu of hyoid ; b.-ky. body of hyoid ; COL. columella ; 

 DNT. deiitary ; EX.OC. ex-occipital ; for. ritag. foramen magnum ; FR. PA. fronto-parietal ; 

 M.MCK. meiito-meckelian ; MX. maxjlta ; N<A. nasal ; Nv. 2, optic foramen ; Nv. 5, 7, fora- 

 men for fifth and seventh nerves ; oc. en. occipital coiidyle ; off. cp. olfactory capsule ; ot. pr. 

 otic process ; PAL. palatine ; pal. qu. palato-quadrate ; /^4.<SP//.tparasp i henoid ; p. c. hy. pos- 

 terior cornu of hyoid ; ped. pedicle ; PMX. premaxilla ; PR.OT. pro-otic ; PTG. pterygoid ; 

 QU.JU. quadrato-jugal ; SP.ETH. sphenethmoid ; SQ. squamosal ; stp. stapes ; VO. yomer. 

 (After Howes, slightly altered.) 



another, and the transverse partition is perforated for the olfac- 

 tory nerves. This very peculiar and characteristic bone may be 

 taken to represent meso- and ecto-ethmoids and pre- and orbito- 

 sphenoids all united together. 



The olfactory capsules (plf. cp) have a delicate cartilaginous roof 

 and floor produced into irregular processes which help to support the 

 olfactory sac. They are separated from one Another by a vertical 

 plate of cartilage, continuous behind with, the girdle-bone and 

 representing the unossified part of the mesethmoid, and the 

 anterior wall of each is produced into a little curved, rod-like 

 rhinal process. The whole of the palato-quadrate arch is un- 

 ossified. 



To this partly ossified chondrocranium the usual membrane 



