270 ZAGLOSSUS. 



largely hitlden by the mylohyoidcus, a thin muscular sheet from the posterior 

 portion of the ramus, beginning some 15 mm. behind the symphysis. The 

 two sheets of opposite sides unite medially by a raphe and insert at the anterior 

 end of the lar3aix. The myloglossus is exposed by laying back the mrjlohyoideus. 

 It is attached on the ventral side of the skull from near the base of the ear on 

 its medial side, forward to the angle of the jaw. It joins the opposite muscle 

 at the midline. 



Muscles of the fore leg. — What appears to represent the deUoideus 

 is present in both the Echidna and the Proechidna as a narrow band arising 

 for a length of about 15 mm. along the anterior edge of the scapula, and at 

 about the same distance dorsal to the junction of the acromion with the cora- 

 coid. It narrows to a round stout tendon, that passes anteriorly to the fore 

 leg to its insertion on the anterior side of the tuberosity of the humerus under- 

 neath the insertion of the pectoral nmscles. This muscle is what Mivart con- 

 siders a second portion of the deltoid, whose main division he regards as the 

 muscle from the clavicle to the pectoral ridge of tlic humerus. As already 

 noted, the homology of this larger muscle is somewhat doubtful. From the 

 fact, however, that in the Proechidna, its origin is wholly from the clavicle 

 and its insertion is continuous with those of the other muscles of the pecioralis 

 group, it seems better to consider it a davopectoralis. 



Owing to the fact that in monotremes the anterior edge of the scapula 

 corresponds to the scapula spine of other mammals, the relations of the muscles 

 in this region differ accordingly. 



The supraspinatus arises from the entire medial surface of the scapula 

 below the insertion of the scrralus. It passes out beneath the acro)nion and 

 episternum and inserts on the anterolateral extremity of the greater tuberosity 

 of the hmiierus. 



The infraspinatus takes origin from the ectal side of the scapula, from 

 the anterodorsal angle to the acromion and nearly to the glenoid cavity. It 

 inserts on the greater tuberosity of the humerus just posterior to the insertion 

 of the supraspinatus and continuous with it. The condition of these muscles 

 in the Echidna is quite similar. 



The subscapularis occupies the entire posterior half of the ectal side of 

 the scapula from the vertebral edge, posterior to the ridge above the glenoid 

 cavity. It becomes tendinous and passes to the extremity of the lesser tuber- 

 osity of the humerus. From the ridge between it and the infraspinatus comes 

 the long head of the triceps. Westling has described in the Echidna a suh- 



