THE BNTIEE SKULL 497 



but is not united to the petrous or the tympanic. The ectotympanic 

 of the auditory bulla is a delicate ring of bone supporting the edge of 

 a large tympanic membrane ; the endotympanic is a membranous sac. 

 The anterior part of the petrous is entirely ossified, except at a cir- 

 cular area on the inferior surface near the apex ; the posterior or 

 mastoid portion is cartilaginous. The malleus is continuous with a 

 rod of cartilage, the so-called Meckel's cartilage, which forms the first 

 trace of the lower jaw and around which the bony mandible is de- 

 veloped from membrane. The petrous appears in the interior of the 

 cranium as an inflated pear-shaped mass of porous bone ; the internal 

 auditory meatus and the hiatus Fallopii are very large ; the aquseduc- 

 tus vestibuli opens in a long groove on the posterior surface ; behind 

 this groove the petrous is still cartilaginous. 



The sphenoid is well formed in bone, and exhibits all its parts. 

 The anterior sphenoid is distinct from the posterior sphenoid ; the pre- 

 sphenoid, however, has united with the orbitosphenoids. The sphe- 

 noidal sinuses are already present. The basisphenoid is separated from 

 the alisphenoids and the pterygoids. The tip of the orbitosphenoid is 

 truncated, and exposes a membranous anterior lateral fontanelle at the 

 pterion between the frontal, parietal, temporal, and sphenoid bones. 

 An area of cartilage between the sphenoid and the petrous and pierced 

 for blood-vessels represents the middle lacerated foramen. 



The frontal bones are very convex ; there are, as yet, no frontal 

 sinuses. The frontal and malar postorbital processes are small tuber- 

 cles. There is no true anterior fontanelle at the bregma. 



On the inner wall of the orbit, below the frontal and above the 

 palatine and maxillary, is a long strip filled by the membrane covering 

 the lateral ethmoid. The lachrymal exhibits only a narrow line of 

 ossification along its anterior border. 



The vomer is for the greater part ossified. The maxillo-turbinal 

 is cartilaginous, except for a small centre of ossification in the partition 

 medial to the lachrymal canal. 



The lateral ethmoids consist of a few folds of cartilage in which 

 have appeared several bony nodules at the anterior end of the future 

 fourth piece, in scrolls 4 and 4' (Fig. 219), and a small nodule in the 

 medial part of the sixth piece. The mesethmoid and cribriform plate 

 are represented by cartilage. The palatines, maxillaries, premaxil- 



laries, and nasals are ossified. 



32 



