Chap. IX.] 



STERNA. 



347 



is known as the sternum. With the anterior end 

 of this sternum there ordinarily comes into relation 

 the ventral part of the anterior limb-arch (see infra) ; 

 and, farther back, we may find the ventral attach- 

 ments of the ribs. In the Chelonia and Ophidia 

 the sternum is lost, and this is to be correlated with 

 the great development of the 

 exoskeleton of the one, and 

 the mode of life of the others 

 of these orders of Reptiles. 

 In the Carinate birds the me- 

 dian portion of the sternum is 

 produced into a long and 

 strong keel (Fig. 145 ; cs), to 

 the sides of which are attached 

 the powerful thoracic muscles 

 which depress and elevate the 

 fore limbs ; an analogous cari- 

 nation is to be seen in Bats. 

 In the fossorial Insectivora, 

 such as the mole (Fig. 146), 

 the presternum is produced 

 far forwards, is keeled, and 

 widened out at the sides so 

 as to afford a large surface 

 of attachment for the mus- 

 cles that move their digging 

 limbs. 



In all the gnathostomatous Yertebrata the body 

 is typically provided with two pairs of lateral ap- 

 pendages, or limbs, one of which lies, as a rule, some 

 distance in front of the other; these are the fore 

 and hind limbs. They are brought into connection 

 with the axial skeleton by means of arches, the 

 pectoral and pelvic arches. 



The Pectoral arch consists essentially of a bar of 

 cartilage, which undergoes division into a dorsal part, 



Fig. 145. Sternum of Fregi- 

 lupus varius. 



cl. Clavicle ; sc, scapula ; co, cora- 

 coid ; cs, keel of sternum. 

 (After Murie.) 



