136 ANATOMY OF THE WOOD RAT 



portion of the skeletal body lengths: in two specimens of 

 Homodontomys, 11.8 and 12 per cent; in two oi Neotoma, 

 12.7 and 13.2 per cent; and in two of Teonoma, 12.6 and 

 13.4 per cent. The slight processes dorsad near the scapular 

 end and ventrad near the sternal end seem not to have been 

 caused directly by muscular action, but rather by the ad- 

 joining articulations. The muscles chiefly concerned with 

 the scapular end of the clavicle are the clavotrapezius, 

 cleidomastoid, and subclavius, and with the medial end, the 

 pectoralis profundus and clavo-acromiodeltoid. 



Scapula. Real length of the scapula, as well as of most 

 other bones, is so variable with age that this item should 

 receive but little consideration. Its length relative to func- 

 tional arm length is more significant, however, but is found 

 to have considerable individual variation. In Homodontomys 

 this figure varies from 42 to 48 per cent, with an average of 

 45; in Neotoma it is from 42.7 to 44.8, averaging 44 per cent; 

 and in Teonoma the variation is from 42 to 47.6 per cent, 

 with 45.2 as an average. There is a tendency for the scapula 

 to be slightly smaller in relation to arm length in the case 

 of younger animals. The width of the scapula, compared 

 with its length, shows slight variation in Homodontomys 

 (from 45 to 47 per cent) and Neotoma (43.5 to 45 per cent), 

 but more in Teonoma (44 to 50 per cent). There is great 

 individual variation in the exact form of the vertebral border 

 of the scapula, chiefly in the region of the coracovertebral 

 angle. 



The lateral surface of the scapula is divided into two parts 

 by the spine. Craniad to the latter is the supraspinous 

 fossa, and caudad, the infraspinous fossa. The axillary 

 border of the latter is considerably raised, probably partly 

 by the influence of the triceps longus and the teres minor 

 originating upon its border, and possibly by the juxtaposi- 

 tion of the teres major. The coracovertebral portion of the 

 supraspinous fossa is usually slightly raised, but is per- 



