ON THE ElMSTERXAL AITARATL'S OF MAMMALS. 559 



tremitiesof the clavicles appear to be directly applied to the obliquely 

 bevelled anterior edge of the manubrium sterni. But an examina- 

 tion of the inner surface of the manubrium shows, that even in 

 this instance, intervening structures are present. (Fig. 10.) 





Episternal apparatus of Scinrus viilgai-is (Squirrel), seen from within: — 

 Sty sternum ; Ep, episteruum ; c, clavicle ; c*, first rib. 



Only a few preparations of the sterno- clavicular articulation are 

 required to show that a remarkable piece is introduced between the 

 sternum and the bony clavicle. This piece is formed of a fibrous 

 mass, which is but slightly developed anteriorly, is softer than carti- 

 lage, and when longitudinal sections are carefully examined, appears 

 to be chiefly composed of connective tissue. The sternal end of 

 the clavicle is here also invested by cartilage, and from the cartilage 

 the fibrous band wdiich can be follow^ed to the sternum directly 

 springs. This band, whilst possessing much firmness in the central 

 part, is of loose texture at the tw^o extremities. The morphological 

 elements of cartilage are not distiDguishable in it, so that on histo- 

 logical grounds the whole intermediate piece is of a difl^'ereut 

 character from tbat which I have found in other mammals. Tamias 

 presents arrangements that are essentially similar to those of Sciurus. 



If the extreme shortness of the parts in the Mole be disregarded, 

 very similar characters are found in the corresponding parts in 

 various Carnivora {Meles, Lutra, Mustela, Felis, Hycsna). Amongst 

 these animals the episternal on each side is represented by a band 

 of considerable length, proceeding from the clavicle, which has been 

 regarded either as properly belonging to the clavicle, partly from 

 defective information, and partly from the similar mode of connec- 

 tion existing between the clavicle and scapula, or, as a structure 

 developed to make up for the smaller size of the clavicle. IS'ow-, 

 although the elongated form and purely ligamentous strcuture of 

 the episternals here present may be considered as a sign of degrada- 

 tion, no objection need be raised to its homology with true epi- 



