CHANGES FOR ADAPTATION IN THE MOLE 349 
inferior crest or spine in Scapanus. This I have verified, and 
have demonstrated a smaller tubercle similarly located in Scalops. 
The scapula possesses a distinct acromion (fig. 11, Ac), from which 
a strong ligament extends to the outer angle of the clavicle. This 
ligamentous connection was described by Bell (’39). There is 
no articulation with the clavicle. 
The proximal end of the scapula articulates directly by means 
of the concave cavitas glenoidalis with the convex facies articu- 
laris scapulae of the humerus. This articular surface has a 
horizontal dimension of 3.8 mm. and a vertical of 1.4mm. This 
gives a very firm articular surface to withstand the pull of the 
powerful muscles of the fore leg. 
The clavicle shows a great modification from the mammalian 
type. It is a strong cube-like bone attached to one of the T-like 
processes at the anterior end of the presternum. It has the 
following dimensions: length 4.1 mm.; anteroposterior 3.1 mm.; 
dorsoventral 6.3mm. As shown in figures 3, 15, and 16, instead 
of the slender elongated bone in man, it has been greatly reduced 
in length, while its other dimensions have been much increased. 
These changes have been necessary to withstand the great strain 
(an end thrust) which is put upon it by the humerus with which 
it articulates. This articular surface is oval with a saddle-like 
depression. It measures anteroposteriorly 3 mm. and dorso- 
ventrally 4.4 mm., thus covering practically the entire distal 
end of the clavicle. When we consider the shape of this surface 
and that of the caput humeri with which it articulates, we must 
conclude that a pivot rotation of the humerus would be very 
slightly if at all possible. The main movements of the humerus 
relative to the axis of the body are forward and backward and 
up and down. Intermediate movements, however, may be made. 
There is a noticeable variation in the clavicle in the five genera 
into which the American moles are divided. These are briefly 
~ described by Jackson (15) as follows: Scalopus: ‘‘clavicle short 
and heavy, about two-thirds as broad as long, penetrated anterio- 
posteriorly through the center by a small foramen.’ Scapanus: 
‘‘elavicle short and heavy, about three-fourths as broad as long, 
distinctly notched on the inferior surface, not penetrated by a 
