MAY, 1921. AMERICAN MARSUPIAL, C^NOLESTES OSGOOD. 33 



portion where its two sides become fused. It arises on the sides and ental 

 surface of the second sternebra and inserts on the thyroid cartilage. 



Mylo-hyoideus. A very thin, paired, transverse muscle between the 

 mandibles and immediately entad of the digastricus. It arises from the 

 inside of the mandible near the alveolar border and has no bony insertion, 

 merely meeting its fellow in a raphe in the median line and becoming 

 aponeurotic anteriorly and posteriorly. Along the dorsal side of this 

 raphe it is attached to the genio-hyoideus. Its posterior fleshy border 

 runs from the angle of the mandible forward to the median line opposite 

 the base of the angular process. 



Hyoglossus. Arises laterad and dorsad of the genio-hyoideus on the 

 ventrocaudal border of the thyrohyals and basihyal cephalad of the 

 insertion of the ihyrohyoideus. It passes ventrad of the ceratohyals and 

 free from them, diverges to enclose the genioglossus, and passes dorsad 

 and cephalad into the body of the tongue. 



Genioglossus. Well-developed and having the usual relations, aris- 

 ing on the sides of the mandibles near the symphysis and forming a 

 wedge between the two halves of the hyoglossus. 



Styloglossus. Runs laterad of the hyoglossus and merges with it 

 about midway of the mandible. Its origin was not determined, having 

 been destroyed inadvertently. 



Thyrohyoideus. Origin on the thyrohyal bone entad of the sternohy- 

 oid and the omohyoid and opposite the hyoglossus. Insertion on the 

 posterior corner of the bony wing of the thyroid cartilage. A short stout 

 triangular muscle, relatively well-developed. 



Omo-hyoideus. Origin on the lateral fourth of the posterior side of 

 the hyoid bone. Insertion on the upper posterior angle of the scapula 

 just craniad of the insertion of the levator scapulae. On the ental side 

 near its origin it is joined to the sternohyoid by thin membrane. 



Sterno-mastoideus . Origin on the manubrium of the sternum slightly 

 overlapped by the edge of the pectoral-is. Insertion divided, one rather 

 thin sheet inserting by broad aponeurosis on the occipital crest from a 

 point midway between the median line and the auditory meatus to the 

 middle of the anterior border of the mastoid bulla. The other division 

 is a thickened bundle and inserts by a short tendon on the mastoid pro- 

 cess slightly ectad and cephalad of that of the cleido- mastoid. The two 

 divisions become fused about midway between origin and insertion. 



Cleido-tnastoideus. Origin on the front of the distal end of the cla- 

 vicle. Insertion fleshy or only slightly tendinous on the mastoid pro- 

 cess. Its outer surface has relation with the splenius, the sterno-mastoid- 

 eus and the cleido-occipitalis; its inner with the digastricus, atlanlo- 

 acromialis and omo-hyoideus. 



