154 ELEMENTARY A NATO AT Y. [LESS 



Even in man's own class the scapula may become much 

 narrowed, as in the Dog; or extremely so, as in the Shrew, 

 and "still more so in the Mole. 



The scapula is entirely osseous in the adult in man, who in 

 this respect agrees with most Mammals and with Birds, 

 but in the majority of lower Vertebrates above Fishes, and in 

 the Ungulata amongst Mammals, the part answering to the 

 posterior border of man's scapula remains permanently, or 

 for a very long time, cartilaginous. In harmony with this 

 condition, we find that the base of the scapula in man long 

 remains a separate epiphysis. This part may be quite 

 distinct, as is the case in the Toad and some Fishes, e.g. the 

 Sturgeon and Raia clavata, where it bears the name of 

 supra-scapula. 



In the fact that the scapula is the great bone of the 

 shoulder, man agrees with the rest of his class ; but its size 

 may be equalled or surpassed by the part answering to the 

 coracoid process, as in many Birds and Reptiles, or it may 

 be reduced to relative insignificance by the much greater 

 development of the clavicle, a 1 ? in most Fishes. 



The scapula (or rather the vertebral portion of it, or supra- 

 scapula), instead of being, as in man, widely separated from its 

 fellow of the opposite side, may be separated from it only by 

 the cartilaginous representative of the spinous processes of 

 the vertebrae, as in Raia clavata; or the two scapulas may 

 overlap the one the other, as in the African toad Dacty- 

 lethra. In the last-mentioned animal the supra-scapula is 

 many times larger than all the rest of the bone. Com- 

 paring the other members of man's class with man, we find 

 that the sub-scapular fossa may be situated (if we define it 

 by the attachment of the subscapularis muscle) not on the 

 inside, as in him, but on the outside of the blade, as is the 

 case in the Echidna. 



The spine of the scapula is a structure constant in man's 

 class, but it may be very little developed, as in the Mole ; or 

 it may be easily overlooked, inasmuch as it forms the actual 

 anterior (in man the upper} border of the scapula in the 

 Monotremes. In these Monotremes its direction is so 

 changed that it lies on one and the same plane with the 

 blade of the scapula ; the supra-spinatus portion of the blade 

 being next the ribs, and the infra-spin atus fossa and sub- 

 scapular fossa together forming its actual outer surface, the 

 axillary margin (which ordinarily separates those two latter 

 fossae) aborting. The spine may be in close juxtaposition to 



