552 



THE NATtlEAL HISTOET EEVIEW. 



into a layer of hyaline cartilage, wliich is separated by a space from 

 the cartilaginous investment of the episternal piece, and thus helps 

 to form or surround a small articular cavity. The investing connec- 

 tive tissue of the episternals, on the other hand, passes on to the 

 sternum without entering into the formation of any articular ca^dty. 



In comparison with other species several peculiarities may here 

 be noticed. In the first place, the elsewhere simple hyaline carti- 

 lage composing the episternals, is separated into tw^o portions, one 

 composed of areolar tissue, and connected with the clavicle ; the other 

 originally cartilaginous, and representing the solid episternals. In 

 the second place the process of calcification of the cartilage has 

 advanced to a considerably greater extent than in other species, the 

 greater part of each episternal being converted into true bone, 

 as is indicated by the presence of numerous medullary areolae, yet 

 even here the bones still constitute osseous nuclei only, since they 

 are invested on each siu'face by a layer of cartilage. 



Tlie episternals of Hi/pudiEus ( H. glareola) are similarly formed to 

 those of the Murida?. The club-shaped clavicle on each side (I'ig. 4.) 



Fig. 4. 



Episternal apparatus of llypudceus glarcolus seen from the inner side: — cp, epis- 

 tenium ; c, clavicle ; c^ first rib ; sf, sternum. 



becomes connected with the hollowed surface of the cartilaginous epi- 

 sternal piece, which contains an elongated bony nucleus, and is but 

 loosely connected to the posterior surface of the very broad manubrium 

 sterni. The division between the clavicle and episternum is very 

 sharply defined throughout the greater part of their line of junction, 

 but at the upper part the cartilage of the episternum is continuous 

 through the intermediation of fibrous tissue Avith the clavicle, and 

 thus an arrangement is exhibited which is betw^ixt that presented by 

 the smaller Muridan and the Eats. 



The episternals of the Soricidse attain nearly the same grade of de- 



