34 



VESTIGIAL EnSTERNA 



provided with pieces of bone which overlie the manubrium sterui 



...a. 



Fio 22.— Shoulder girdle of Ornithorhynchus. c\ c'-, c^, First, second, third ribs ; d, 

 ' clavicle ; e.c, epicoracoid ; es' and es", interclavicle (episternum) ; »)..<•, metacoracoid ; 

 ni.s, manubrium sterni ; sc, scapula ; st, sternebra. (From Wiedersheim's Structure 

 of Man.) 



and are attached to the clavicles, and are no doubt to be regarded 



as the same structure. Prolmbly in many 

 mammals the manubrium will be found 

 to be partly made up of corresponding 

 rudiments. In any case, vestiges of au 

 episternum in the shape of two minute 

 ossicles have been discovered in Man, 

 lying in front of the manubrium. They 

 have been termed ossa suprasternalia. 

 In llan and in the Mole the paired 

 nature of the episternum is clearly 

 apparent. It has been suggested that 

 this structure in its entirety belongs to 

 the clavicles, just as the sternum belongs 

 to the ribs ; i.e. that it formed out of the 

 approximated and fused ends of the 

 clavicles. Dr. IMivart ^ figured a good 

 many years since a pair of ossicles in 

 Mycetes, lying in one case between the 

 ends of the clavicles and the manubrium 

 sterni, and in another example anterior 

 to the ventral ends of the clavicles. fJegenbaur has figured a 



Fig. 23. — Ei>isternum of an em- 

 bryo Mole, (After A. Gdtte. ) 

 (.'?, Clavicle ; es', central jior- 

 tion of the episternum ; es'\ 

 lateral portion of the same ; 

 r.c, costal ribs ; st, sternum. 

 (The figure "was constructed 

 from two consecutive hori- 

 zontal sections.) (From 

 Wiedersheim's Structure of 

 Mail.) 



Proe. Ziiol. Soc. 186.5, p. 567. 



