252 THE VERTEBRATE SKELETON. 



The Olfactory capsules and associated bones. 



Two pairs of membrane bones, the vomers and nasals, are 

 developed in association with the olfactory organ, but the 

 mesethmoid is not ossified. 



The vomers form a pair of delicate bones, each consisting of 

 a vertical plate (fig. 45, 15), which with its fellow separates 

 the two narial passages, and of a horizontal plate which forms 

 much of their roof. The vomers articulate with one another 

 and with the pterygoids, palatines, and maxillae. 



The nasals (fig. 45, 2) are very long narrow bones extend- 

 ing along the middle line from the frontal almost to the 

 anterior nares. They are continuous laterally with the pre- 

 maxillae, maxillae, lachrymals and prefrontals. They form 

 the roof of the narial passages. 



3. THE UPPER JAW AND SUSPENSORIAL APPARATUS. 



These are enormously developed in the Crocodile and are 

 firmly united to the cranium. It will be most convenient to 

 begin by describing the bones at the anterior end of the jaw 

 and to work back thence towards the brain-case. The most 

 anterior bones are the premaxillae. The premaxillae (figs. 44 

 and 45, 1) are small bones, each bearing five pairs of teeth, 

 set in separate sockets in their alveolar borders. They con- 

 stitute almost the whole of the boundary of the anterior 

 nares, which are confluent with one another and form a 

 large semicircular opening in the roof of the skull, leading 

 into the wide narial passage. They are also partially sepa- 

 rated from one another in the ventral middle line, by the 

 small anterior palatine vacuity (fig. 43, A, 8). They form 

 the anterior part of the broad palate. The alveolar border 

 on each side between certain of the teeth is marked by pits 

 which receive the points of the teeth of the other jaw. The 

 first pair of these pits in the premaxillae are often so deep as 

 to be converted into perforations. Pits of the same character 

 occur between the maxillary and mandibular teeth. 



