4H MANUAL OF ZOOLOGY sect. 



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 mem- 

 brane bones, the small premaxilla (PMX) in front, then 

 the long narrow maxilla (MX), and finally the short quad- 

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

 the quadrate. The mandible contains on each side a per- 

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

 anterior end, outside which are two membrane bones. The 

 hyoid is a squarish plate of cartilage (/>. hy) with two pairs of 

 processes (a.c. Ay, p. c.hy), the posterior of which is ossified. 



The scapula is ossified and is connected j^y its dorsal 

 edge with a supra-scapula (Fig. 247, S. SCP) formed partly 

 of bone, partly of calcified cartilage, and developed from 

 the dorsal region of the embryonic shoulder-girdle. The 

 coracoid (Fig. 249, Co) is also ossified, while the procora- 

 coid is represented by a bar of cartilage, having a membrane 

 bone, the clavicle (CI), closely applied to it. The supra- 

 scapula overlaps the anterior vertebra; ; the coracoid and 

 procoracoid are connected ventrally by a cartilage, the epi- 

 coracoid (Co'), which is in close contact with its fellow of 

 the opposite side in the middle ventral line, so that the 

 entire shoulder-girdle, like that of the dogfish, forms a 

 single inverted arch. 



