546 



THE NATURAL HISTOEY REYIEW. 



present in the Armadilloes have sometimes been met with in man, 

 the analogies of the several parts have certainly not been accurately- 

 followed out. The results of my investigations show that episternal 

 bones, or bones analogous to them, are much more commonly present 

 than is usually admitted, and I am inclined to think that an examina- 

 tion of their arrangement in different animals may throw some light 

 on their morphological significance. The degree of development at' 

 tained by the episternal structures in different mammals undoubt- 

 edly varies to a considerable extent ; .and I shall therefore first 

 describe the highly developed condition of these parts, presented by 

 the Monotremata and Armadilloes, and leave to a subsequent period 

 the discussion of the relatively smaller and therefore less easily 

 recognized examples met w^ith in other animals. 



Amongst the Marsupials, I find in several species of Didelpliys a 

 T-shaped cartilaginous piece, the expanded base of which is seated 

 on the anterior extremity of the sternum, and which in one case 

 extended so far on either side as to assist in forming a j^oint 

 d'appui for the first rib. This structure (Ep. fig. I.) might indeed be 



Fig. 1. - .....; 



cl ^j, ci ^ ti oonarfw 



iiifiibenr ©rf;^ \ 



Episternal apparatus of Bvlelphys (Opossum.) :—&t, sternum ; cj>, episternum ; 

 cl^ clavicle ; c, rib. 



regarded as a persistently cartilaginous manubrium sterni ; but tbe 

 two transverse arms, proceeding from its anterior attenuated 

 extremity, render this explanation doubtful. Moreover the connection 

 of the lateral basal process with the first rib is by no means constant : 

 indeed in various examples of three species of Bideli^hys that I 

 examined, it was only met with in one instance, (shown in Fig. I.) 

 The transverse anterior arms are club-shaped at their extremities, 

 and are applied by their posterior or upper surfaces to the some- 

 what swollen extremities of the clavicles. On making traiisverse 

 sections it may be clearly shown that there is an articular cavity 



