XIII 



PHYLUM CHORD ATA 



299 



bearing the ventral half ( >f the glenoid cavity (glen) for the head of 

 the humerus ; a large gap or fenestra divides each into a narrow 

 anterior portion the pro-coracoid (pr. cor) and a broader posterior 

 portion, the comcoid proper (cor}. The scapulce (sc) articulate 

 with the outer ends of the coracoids, and each bears the dorsal half 

 of the glenoid cavity. Dorsally the scapulas become expanded, and 

 each has connected with it a thin plate of partly calcined cartilage 

 -the supra-scapula (supra, sc), which extends inwards towards the 

 spinal column on the dorsal aspect of the body. An element 

 not hitherto met with is the interclavicle or episternuw (epist), 

 a cross-shaped membrane bone, the stem of which is longi- 

 tudinal and closely 

 applied to the ven- 

 tral surface of the 

 sternum, while the 

 cross-piece is situ- 

 ated a little in front 

 of the glenoid cavi- 

 ties. The clavicles 

 (cl) are flat curved 

 bones articulating 

 with one another 

 in the middle line 

 and also with the 

 anterior end of the 

 interclavicle. The 

 bones of the fore- 

 limb consist of a 

 proximal bone or 

 humerus, a middle 

 division composed 

 of two bones the 

 radius and ulna, 

 and a distal divi- 

 sion or manus. In 



the natural position of the parts the humerus is directed, 

 from the glenoid cavity with which it articulates, backwards 

 upwards and outwards ; the radius and ulna pass from their 

 articulation with the humerus downwards and slightly forwards, 

 while the manus has the digits directed forwards and outwards. 

 When the limb is extended at right angles to the long axis of the 

 trunk, it presents, like that of the Frog, dorsal and ventral surfaces, 

 and pre-axial and post-axial borders. In this position the radius 

 is seen to be pre-axial, the ulna post-axial. In the natural position 

 the pre-axial border of the humerus is external, and the distal end 

 of the forearm is rotated in such a way that, while the pre-axial 

 border looks forwards and outwards at the proximal end, it looks 



Fit.. '.'Os. Pectoral arch and sternum of Lacerta agilis. 

 i-l . clavicle ; <:or. coracoid ; cp. co/-. epicoracoid ; tpist. epi- 

 sternum ; <//<-n. glenoid cavity for head of hurnerus ; pr. 

 '":. pro-coracoid ; rl. / -4 . first to fourth sternal ribs ; 

 sc. scapula ; si. sternum ; supra, sc. supra-scapula. (After 

 Hoffmann.) 



