254 Mammalia. 



Basioccipital, Basisphenoid, Presplieiioid, and Ethmoid ; the 

 roof being formed by the Frontal, Parietal and Supraoccipital, 

 which have been cut away. The Ethmoid bone consists of 

 two perforated parts and a median partition, the perforated 

 parts being opposite to, and transmitting the olfactory nerves 

 arising from the olfactory lobes. That which comes into 

 view under the vertical section is the middle plate, or * lamina 

 perpendicularis' of the Ethmoid bone; and its prolongation 

 forwards, as the median cartilaginous septum of the nose. 

 Considering this septum to be a continuous structure, ossified 

 in the neighbourhood of the cribriform plates, but not ossified 

 beyond the first inch and a-half from the cranium. Professor 

 Flower applies the term ' Mesethmoid' to the whole of this 

 element of the skull, whether ossified or not, including the 

 'crista galli' of human anatomy. On either side of this 

 Mes-ethmoid are the Turbinal bones, contained in either 

 nasal cavity. These Turbinals are formed by two distinct 

 sets of convoluted spongy bony plates ; a lower set, which 

 come close down to the nasal orifice, and which are 

 attached to the Maxilla by one of their folds, whence they 

 are called Maxillo- turbinals, and an upper set, extending 

 from the cribriform plate to the posterior and superior mar- 

 gin of the Maxillo-turbinals, from which however they are 

 quite distinct and separate, and called, from their attach- 

 ment to the cribriform, ethmoid, or sieve-like plate, the JEfh- 

 mo- turbinals. " It will be observed* that while the Ethmo- 

 turbinal is placed high in the nasal cavity, and above the 

 direct channel by which the air passes to the posterior nares, 

 the Maxillo-turbinal, situated near the front of the chamber, 

 before it has divided into an upper true olfactory chamber 

 and a lower nasal passage, nearly blocks up the whole cavity, 

 so that air passing through in inspiration is filtered between 



* Flower. Ost. Mam. p. 108. 



