156 ELEMENTARY ANATOMY. [LESS. 



and the clavicle is constant in mammals where the latter bone 

 is developed, except in the Mole and Three-toed Sloth. In 

 the Mole, however, there is a strong ligamentous connexion 

 between these parts, and in the Three-toed Sloth the sepa- 

 ration is a secondary condition, owing to the gradual atrophy 

 of the acromion which was primitively connected with the 

 clavicle. 



The supra-spinatus fossa may be about equal to the infra- 

 spinatus one, as in the Dog and Shrew, or larger than it, as 

 in the Lion and in Sloths. It may, on the contrary, be little 

 more than a groove, as in the Dolphin, or it may (and this is 

 very exceptional) be large and situate entirely on the inner 

 (or body) surface of the blade, as in the Echidna. 



FIG. 130. RIGHT SCAPULA AND FIG. 131. SCAPULA OF A PORPOISE. 



If^-Slrfl (If^SeT * " *" <" ; ' SlM id 

 a, acromion ; c, coracoid ; cl t clavicle ; 

 ma, metacromion ; mss, meso-sca- 

 pular segment. 



The portion for the origin of the teres major muscle may 

 be greatly produced, as in the Armadillos and even in 

 Baboons. 



The superior border of the scapula may be very much 

 longer than the base, as in Ungulates, and enormously so in 

 the Mole. It may, on the contrary, be relatively shorter even 

 han in man, as in the Chimpanzee. It may be very convex, 

 as in the Mandrill Baboon ; and, most strange of all, it may 

 form what is apparently the posterior margin of the scapula, 

 as in the Echidna. 



The supra-scapular notch may be converted into a foramen, 

 as even in one of man's order (e.g. in Mycetes), and in the Two- 

 toed Sloth. The notch, however, may be entirely absent, as 

 in the Deer and many others. 



The base may be much the shortest of the three borders, 

 as in the Dog and Ungulates, and especially in the Mole. It 



