m SKULL 43 



The upper jaw is formed of three bones on either side. In 

 front is the premaxilla (P. MX), a short bone, sending off 

 an upward process towards the nostril. Next follows the 

 maxilla (MX), a long, curved bone, forming the greater 

 part of the upper jaw, and joined at its posterior end to a 

 small, slender bone, the quadrato-jugal (QU.JU), which is 

 firmly connected with the lower end of the suspensorium. 

 Both premaxilla and maxilla are produced below into a 

 prominent edge from which spring a number of small 

 conical teeth, arranged in a single row. 



Besides these three bones there are two others which 

 seem, as it were, to brace the upper jaw to the brain-case 

 and suspensorium. The palatine (PA L) is a narrow, rod- 

 like bone, placed transversely behind the olfactory capsule. 

 The pterygoid (PTG) is a large three-rayed bone ; one ray 

 is directed forward and connected with the outer end of the 

 palatine and with the inner face of the maxilla ; another 

 passes backwards and inwards and is connected with the 

 auditory capsule ; the third extends backwards and out- 

 wards and forms the inner and ventral portion of the sus- 

 pensorium. The main mass or core of the suspensorium, 

 between the squamosal outside and the pterygoid within, 

 is a rod of cartilage (sus), which is continued forwards by a 

 bar (pal. qii) supporting the pterygoid and palatine. 



There is an important distinction to be drawn between the 

 bones of the skull which can be made out only by the 

 exercise of a good deal of care and patience. By softening 

 the connective-tissue which binds the bones together, it is 

 possible to remove the majority of them without injuring 

 the underlying cartilage (compare the right and left sides 

 of the skull in Figs. 8 and 9, A and C), provided, of course, 

 that the operation is skilfully performed : these bones are the 

 nasals, vomers, fronto-parietals, parasphenoid, premaxilla?, 

 maxillae, quadra to-jugals, palatines, pterygoids, and squa- 

 mosals. A sort of foundation or groundwork (left side of 

 figure in Figs. 8 and 9, A ; right side in Fig. 9, C) is then left 

 behind, consisting mainly of cartilage, but containing the 

 exoccipitals, pro-otics, and girdle-bone. These five bones 

 cannot be removed without pulling the cartilaginous ground- 

 work or chondrocranium to pieces. We thus get a distinc 

 tion between replacing bones (" cartilage bones ") which are 

 actually continuous with the cartilage and form part of the 

 chondrocranium, and investing bones (" membrane bones ") 

 which lie outside the chondrocranium, united to it only by 

 connective-tissue. 



The chondrocranium has a cartilaginous roof, underlying 

 the fronto-parietals ; it is pierced by one large (Fig. 8, fon) 



