EMERSON: ANATOMY OF TYPHLOMOLGE. 
61 
end, inserting posterior to it on the mandible. The action of these 
two muscles is to close the jaws. 
The digastric (cephalo-dorso-maxillaris) is a large thick muscle 
arising by two heads, one from the parietal, postero-lateral to the 
masseter, the other from the anterior border of the distal end of the 
first epibranchial, posterior to the cerato-hyoideus externus. Both 
heads uniting, insert on the mandible posterior to its articulation. 
The action of this muscle is to open the jaws. 
The mylo-hyoideus (intermaxillaris anterior) is a thin delicate 
sheet arising from the inner ventral surface of the anterior half of 
the mandible and inserting with its fellow in the mid-ventral line. 
The stylo-hyoideus (intermaxillaris posterior) consists of two 
parts. The anterior, a delicate fan-shaped sheet, arises from the 
anterior border of the distal end of the hyoid and inserts with its 
fellow in the mid-ventral line, covered by the mylo-hyoid. The 
posterior part is a somewhat thicker sheet arising from the pos¬ 
terior border of the distal part of the first epibranchial, median to 
the insertion of the cerato-hyoideus externus, and inserting like the 
anterior part and posterior to it. These two intermaxillary muscles 
serve to hold the hyoid apparatus more firmly in place and by their 
contraction and expansion it can be raised and lowered slightly to 
allow for the fluctuation of the throat in breathing. 
The genio-hyoideus is a very long and slender, paired muscle 
arising from the inner surface of the mandible near the symphysis, 
covered by the intermaxillaries, and inserting on the posterior end 
of tiie second basibranchial. As seen from the ventral aspect, it 
forms a conspicuous double band lying in the median line. 
Muscles of the Hyoid Apparatus. 
The muscles of the hyoid apparatus are much like those of Nec- 
turus and Proteus, the most important difference being the presence 
of a levator arcus primi which is attached to the first epibranchial. 
Tiie ventral aspect shows the following muscles: — 
The cerato-hyoideus externus is the largest of the hyoid muscles. 
It arises from tiie antero-proximal border of the ventral surface of 
the hyoid and is inserted on the anterior border of the distal end of 
the first epibranchial, median to the origin of the second head of 
the digastric. 
