410 MANUAL OF ZOOLOGY SECT. 



ossification of somewhat complex form, which lies partly in 

 the wall of the anterior portion of the cranial cavity, partly in 

 the wall of the posterior portions of the nasal cavities or 

 olfactory sacs. 



To this cartilaginous cranium with its cartilage bones 

 certain membrane bones are added. Covering the roof 

 of the brain-case are two long narrow bones called the 

 fronto-parietals (FR.PA), because they are formed by the 

 union of a pair of frontals in front with a pair of 

 parietals behind. Over the olfactory capsules are a pair 

 of triangular nasals, (JVA.) and applied to their ventral 

 surfaces small paired vomers ( VO.} On the ventral surface 

 of the skull is a large T-shaped parasphenoid, (PA.SPtf.) its 

 stem underlying the base of the cranium, while its two arms 

 extend outwards beneath the auditory capsules. 



The palato-quadrate cartilage is unossified : but in relation 

 to its anterior portion is a palatine (PAL) membrane bone 

 and to its posterior portion a pterygoid (PTG). The former 

 is a slender rod-like bone directed transversely on the lower 

 surface of the skull. The latter is a larger three-rayed bone 

 having an anterior, an inner, and a posterior arm. The 

 posterior portion of the palato-quadrate cartilage the quad- 

 rate or suspensorium sus connects the lower jaw with the 

 posterior region of the skull. Internally it is covered over 

 by the inner and posterior arm of the pterygoid : externally 

 a hammer-shaped membrane bone, the squamosal (SQ) 

 is applied to it. The upper jaw is formed by three 

 membrane bones, the small premaxilla (PMX) in front, 

 then the long narrow maxilla (MX), and finally the short 

 quadrato-jugal (QU.JU) which is connected posteriorly with 

 the quadrate. The mandible contains on each side a 

 persistent Meckel's cartilage as a sort of core, ossified at its 

 anterior end, outside which are two membrane bones. The 



