219 



LECTURE XII. 



ON THE STRUCTURE OF THE SKULL. 



THE SKULLS OF REPTILIA AND AVES. 



The skulls of those abranchiate Vertebrata which do not 

 suckle their young, and are oviparous, or ovo-viviparous, pre- 

 sent certain peculiarities of construction in which they all agree 

 with one another, and differ from the branchiate Vertebrata on 

 the one hand, and from the Mammalia on the other. 



Thus, the basi-occipital and the basi-sphenoid are always well 

 developed, and the former furnishes a large part of the occipital 

 condyle, which is single and central. 



There is no parasphenoid, or median membrane bone, under- 

 lying the base of the skull. 



The lower jaw, each ramus of which is composed of several 



pieces, articulates with the quadrate bone, as in the branchiate 



Vertebrata ; but the quadrate bone articulates directly with the 



cranial wall, and is not . separated from it by any structure 



representing the hyomanclibular bone. 



It may probably be added that the basi-sphenoid is formed by 

 the union of three ossifications of cartilage — one supero-median 

 and two infero-lateral (the basi-temporals of Mr. Parker) ; but 

 further research is required before this generalization can be 

 regarded as firmly established.* 



* The caution expressed in the text seems to be no longer necessary, as my 

 friend Mr. Parker, who possesses a remarkably extensive knowledge of the details 

 of the structure and development of the vertebrate cranium, informs me that he has 

 now found " the median basi-sphenoid and the symmetrical basi-temporals in 

 Ophidians, Anguians, Scincoids, Iguanians, Geckos, Chamaeleons, Cyclodonts, Lacer- 



