THE GREAT ANTEATER. 127 



arch. Supposing the stylohyoideus to contract one-third of its length, it would protract 

 the hyoid arch to the same extent : in which act it combines with the geniohyoideus. 

 The retraction of the hyoid arch is provided for by the sternothyroidei (PI. XXXVIII. 

 fig. 1 , p) and their apparent continuations the thyrohyoidei. There is no direct sterno- 

 hyoid muscle : the homologue of this seems to be the sternal portion of the sterno- 

 glossus {ib. g). 



Geniohyoideus. — This muscle arises by a single tendon from the symphysis of the 

 jaw. It is one line in breadth, flat, runs back beneath the raph^ of the anterior 

 mylohyoideus ; slightly expands beneath the raph^ of the middle mylohyoideus, then 

 again contracts and again expands, and at about ten inches from its origin becomes 

 diffused into fleshy fibres, which gradually acquire a breadth of six lines, continue 

 back in close connexion with the mylohyoideus to the commissural tendon (*, fig. 2) 

 and there expand, the lateral borders being attached thereto. Here a mid-line of 

 separation appears, and the muscle bifurcates into two flat fasciculi (PI. XXXVII. 

 figs. 1 &2,l, I) each six lines broad, which are inserted into the angles of the basihyal. 



The Sternothyroidei (PI. XXXVIII. fig. 2, p, p) come off' from the inner and lateral 

 parts of the sixth, seventh and eighth sternal bones, and from the seventh and eighth 

 sternal ribs near their articulations therewith. The interthoracic extent of these muscles 

 is six inches. At about two inches from the origin is the point of a tendinous angular 

 intersection (*), somewhat more marked than in the sternoglossus ; the angle is turned 

 forward on the opposite side of the muscle. These intersections vary somewhat in the 

 two muscles, the left sternothyroideus presenting two within the chest, the right one 

 three. Behind the manubrium the left muscle sends off" a small fasciculus of fibres to 

 the right one, and the right reciprocally to the left. Where the decussation takes 

 place there is a tendinous intersection at the fore part, which does not extend to the 

 back part of the muscle. In advance of the interchange of fasciculi the sternothyroidei 

 diverge, increase in thickness, and decrease in breadth just before they emerge from 

 the chest ; beyond which cavity they are fleshy throughout their extent {ib. fig. \,p,p), 

 and are inserted into the lower and fore part of the thyroid cartilage {ib. q). 



Cricothyroidei. — These muscles (PI. XXXVIII. fig. 1, r, r) cover the whole of the 

 cricoid cartilage, beneath and external to the sternothyroidei, and are inserted into the 

 lower and lateral borders and productions of the thyroid cartilage. 



The Thyrohyoidei (PI. XXXVIII. fig. 2, s, s) arise from the lateral and anterior parts 

 of the thyroid cartilage, above the preceding, and are inserted into the median two- 

 thirds of the thyrohyal or posterior horn of the hyoid. 



The Intercornualis (PI. XXXIX. fig. 2, q) is a straightened mass of fibres passing 

 obliquely from the thyrohyal forwards and inwards to the epihyal. 



A ligament connects the mesial end of the ceratohyal with the anterior and outer end 

 of the thyrohyal. A shorter and thicker ligament ties the posterior and outer end of 

 the thyrohyal to the thyroid cartilage. 



