THE FORELIMB. 31 



58. The Pectoral Arch consists on each side of two 

 pieces. On the articulated skeleton note its general 

 position with respect to carapace and plastron, and the 

 attachment of the forelimbs to its outer angles. 



59. One of the pieces of the pectoral arch on each 

 side {the scapiilo-precoracoid) is V-shaped, with the angle 

 of the V turned outward. Its dorsal limb (scapula) is 

 longer than the other and attached to the ventral as- 

 pect of the first costal plate, opposite the first dorsal 

 vertebra. 



60. The precoracoid, which forms the shorter and ven- 

 tral limb of the V, nearly meets its fellow in the middle 

 line opposite the entoplastron (19) ; in the recent state, 

 stout ligaments attach it to the plastron. 



61. The remaining bony piece of the pectoral arch 

 on each side is the coracoid bone ; it is somewhat flat- 

 tened dorso-ventrally, and passes back in a nearly hori- 

 zontal plane from its articulation with the scapulo- 

 precoracoid where the two limbs of the V formed by 

 the latter meet. Its posterior end is expanded. 



62. Note the dee'p glenoid fossa where the elements 

 of the pectoral arch meet. 



63. When you open another terrapin (77) observe 

 the stout ligament joining the distal ends of coracoid 

 and precoracoid ; it represents the epicoracoid, found 

 as a distinct bone in some reptilia. 



64. The Forelimb is short and stout. Note in the ar- 

 ticulated skeleton that it lies in a nearly horizontal 



