SKELETON OF THE CROCODILE. SENSE CAPSULES. 251 



side-view of the skull ; it is bounded on its inner side by the 

 periotic bones, posteriorly in part by the exoccipital, and else- 

 where mainly by the quadrate. A large number of canals 

 and passages open into it. On its inner side opening ventro- 

 anteriorly is the fenestra ovalis, opening ventro-posteriorly 

 the internal auditory meatus (fig. 45, \ T III), while dorsally 

 there is a wide opening which forms a communication through 

 the roof of the brain-case with the tympanic cavity of the 

 other side. On its posterior wall is the prominent foramen 

 through which the facial nerve passes on its way to its final 

 exit from the skull through the exoccipital, this foramen is 

 bounded by the quadrate, squamosal, and exoccipital. 



The opening of the fenestra ovalis is in the fresh skull 

 occupied by the expanded end of the auditory ossicle, the 

 columella, whose outer end articulates by a concave facet 

 with a trifid extracolumellar cartilage which reaches the 

 tympanic membrane. The lower process of this extracolumella 

 passes into a cartilaginous rod which lies in a canal in the 

 quadrate and is during life continuous with Meckel's cartilage 

 within the articular bone of the mandible. 



The columella and extracolumella are together homologous 

 with the chain of mammalian auditory ossicles. 



The Optic capsules and associated bones. 



Two pairs of bones are associated with the optic capsules, 

 viz. the lachrymals and the supra-orbitals. The lachrymal 

 (fig. 44, 3) is a fairly large flattened bone lying wedged in 

 between the maxilla, nasal, jugal, and prefrontal. It forms a 

 considerable part of the anterior boundary of the orbit, and is 

 pierced by two foramina. On the orbital edge is a large hole 

 leading into a cavity within the bone which lodges the naso- 

 lachrymal sac, and communicates with the narial passage by 

 a wide second foramen near the anterior end of the bone. 

 The supra-orbital is a very small loose bone lying in the eyelid 

 close to the junction of the frontal and prefrontal. 



