of the Skull and the Skeleton. 361 



So far, then, in its general plan the skull follows the vertebral 

 type. But by the narrowing down of the bronchial tube, and 

 the resistance of the surrounding organs, the mouth below and 

 the brain-case behind, a powerful ossifying force, of which we 

 have already seen evidence in the trachea, comes into play, 

 different to that of the chest; for there the digestive canal is 

 enclosed by the breathing-apparatus, while here the breathing- 

 canal is small, and nearly shut in by the digestive canal below 

 and by the resisting vertebral centrum above. So that, seeing 

 what the result of the thoracic action was in the development of 

 ribs and in the development of the trachea, it must be antici- 

 pated that ossifications will likewise take place in the skull from 

 the same cause in the direction of greatest resistance, i.e. above 

 and below the termination of the trachea in the skull; and accord- 

 ingly we find a triple series of bones above and in front, and 

 another triple series below and behind. The first series consists 

 of the nasal bones, the ethmoid,- and the vomer, the nasal bones 

 and vomer being in the position of epiphyses of the ethmoid ; 

 and below these are the pterygoid and palatine bones, and an 

 unossified blastemous extension of the latter anteriorly, on which 

 the maxillary and premaxillary bones are developed, just as the 

 prehensile bones of the lower jaw were developed on a cartila- 

 ginous extension. This, then, is clearly a distinct region of the 

 skull, to which there is obviously nothing even analogous in a 

 vertebra ; and in reviewing its comparative osteology, I find no 

 reason for considering it less a fundamental essential of a deve- 

 loped skull than the neural region itself. And just as the brain- 

 ease is known as the neural region, so this part may well be 

 called the bronchial region ; for just as the former is a modified 

 neural arch and its centrum, so the latter is a modified termina- 

 tion of the trachea : and thus, although the skull appears in this 

 matter to deviate from our conception of a vertebra as merely 

 an ossified structure, yet it conforms even in that deviation to 

 the plan of a segment of the body, and so brings the skeleton 

 into a closer and more natural unity. 



The lower jaw and its upper appendages being a modified rib, 

 we thus exhaust all the vertebral elements without accounting 

 for the maxillary or premaxillary, or the distal elements of the 

 lower jaw exterior to MeckeFs cartilage. The maxillaries, by 

 development no less than by function, are the anterior epiphyses 

 of the palatines ; while the premaxillaries appear to be the lateral 

 epiphyses of the ethmoid. Such is the circumstance of their 

 origin, though no doubt their development is due to the same 

 pressure by which we have seen that all bones are formed. Thus 

 in the elephant, where the premaxillaries have to support the 

 enormous tusks, they attain an enormous development, covering 



Ann. (?f Mag. N. Hist. Ser. 3. Vol. xviii. 25 



