The Skull of Notothalamus Torosus 



Sarah Marimon 



There are twenty-eight bones in the entire skull of Notothal- 

 amus torosHS. There are, however, only fifteen different kinds, 

 since thirteen are paired. 



These paired bones are : nasals, ectethnoids, maxillaries, fron- 

 tals, parietals, squamosals, quadrates, ptergoids, occipitals, squamo- 

 palatines, sphenethnoids, and (of the mandible) dentaries and artic- 

 ulaires. 



The unpaired bones are: the parasphenoid and the premax- 

 illary. 



The premaxillary ( 1 ) is the bone which forms the external 

 division between the two nares. It consists of a rather thin 

 dividing bone, which broadens out to form a broad flat base. Dor- 

 sally the dividing bone diverges posteriorally to form two slender 

 processes which join at the ends with the premaxillary processes of 

 the frontal bones, and articulate on the exterior sides with the two 

 nasal bones. Ventrally the dividing bone broadens out suddenly 

 into a broad flat base which forms the most forward portion of the 

 roof of the mouth, and serves as a connection between the two 

 maxillaries. 



The nasals (2) are two irregularly shaped bones, each of which 

 articulates on the interior side with a premaxillary process, on the 

 exterior side of the ectethnoid and the maxillary. Anteriorally 

 the nasals bound the dorsal side of the nasal cavity. 



The ectethnoids (3) are two triangular bones located on either 



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FIGURES 

 In lettering- these figures I have used the following method: 

 Each bone on the skull is marked with a large number. Throughout the 



figures, each bone goes by its number. When an articulation with a certain 



bone is indicated a small figure is used. The bone itself bears a large figure. 



When the bone borders on a cavity, or has a free edge, that portion of the 



bone is not numbered. 



Upper or outer surfaces are indicated by numbers, under or inner surfaces 



are indicated by the same numbers prime (1). 



