96 THE STERNUM. [CHAP. 



As the clavicle is supported at the anterior extremity of 

 the elongated presternum, it is widely separated from the 

 first rib, and the anterior extremities are brought into such 

 close juxtaposition with the head that the animal appears to 

 have no neck. 



In the CHIROPTERA, the sternum presents a considerable 

 general resemblance to that of Man. The presternum is 

 large, trilobate in front, and strongly keeled. The meso- 

 sternum is likewise frequently strongly keeled (Pteropus, 

 Cynonycteris), but this keel is separated from that of the 

 presternum by a deep notch. In many of the Insectivorous 

 Bats the segments of the mesosternum are (at least in adults) 

 firmly ankylosed together, but in some of the frugivorous 

 Bats (Pteropus, &c.) they continue separate. 



In the RODENTIA, the sternum is long and narrow, consist- 

 ing of a presternum (which is generally broad in the forms 

 which have the clavicle well developed, as the Rats, Beavers^ 

 &c.), a mesosternum of three, or more usually four 5 seg- 

 ments, and a long xiphisternum, with a broad cartilaginous 

 terminal expansion. The segments of the mesosternum 

 often have epiphyses at each end. 



The presternum is compressed and produced forwards in 

 those species in which the clavicle is absent or rudimentary, 

 as the Aguti, the Hares, and the Capybara. In the latter it 

 much resembles that of the Horse or Tapir. 



Order UNGULATA. In the Ruminantia there are usually 

 seven segments altogether in the sternum (Fig. 35). The 

 presternum is narrow, rounded in front, and bearing the first 

 pair of sternal ribs close to its apex. The succeeding pieces 

 gradually widen, the posterior segments of the mesosternum 

 being square, flat, and rather massive (especially in the 

 Giraffe) ; they are hollowed at the middle of their lateral 

 borders. The xiphisternum is thin and flat. 



