384 



ANATOMY OF VERTEBRATES. 



the inner surface of the scapula. Both the acromion and coracoid 

 are well developed. 



The humerus is perforated above the inner condyle : this is a 

 tuberosity which appears to be supported by four converging 

 columnar ridges or processes. The deltoid and supinator ridges 

 are well marked. The shaft of the ulna is much compressed : its 

 distal portion coalesces with that of the radius. In the carpus 

 an accessory ' intermedium ' is wedged between the scaphoid and 

 trapezium. The bones of the pollex support the tubercle that 

 outwardly represents that digit ; the Squirrel's favourite nut is 

 mainly held between the ' thumb tubercles ' when operated on 

 by the chisel-teeth. In the pelvis the epicotyloid tubercle is 

 strongly developed : the ilia articulate with the first sacral ver- 

 tebrae exclusively, but the ischia abut against the long transverse 

 processes of the first caudal: beyond this vertebra the ischia 

 develope on each side two tuberosities, one at the usual place, 

 the other and stronger one near the lower end of the symphysis. 

 The femur shows an almost equal developement of the three 

 trochanters. The medullary artery enters on the inner side of 

 the shaft, just below the small trochanter. 



The tibia and fibula coalesce distally. There is an inter- 

 articular ossicle in the knee-joint; a patella; and two fabellag. 



one behind each femoral condyle. In the tarsus an 

 accessory ossicle is wedged between the calcaneuni; 

 astragalus, naviculare, and entocuneiforme. 



The little Flying Squirrel {Pteromys volucella), fig. 

 247, is chiefly remarkable for the long and strong accessory carti- 

 lage, a, projecting from the ulnar side of the carpus, which aids 

 in supporting the lateral fold of integument serving as a para- 



