320 CALIFORNIA ACADEMY OF SCIENCES [Proc. 4th Sek. 



The mylo-hyoid or platysma myoides is poorly developed 

 in Anolis and is visible only under the dissecting microscope 

 or in microscopical cross sections. It is a thin sheet having 

 its origin along the mandible and inserting in a median raphe. 

 (Fig. 3.) 



The second layer consists of four muscles, namely, the 

 genio-hyoid, mandibulo-hyoid, sterno-hyoid and omo-hyoid. 

 (Figs. 3, 4.) 



The genio-hyoid is a thin strip of muscle tissue extending 

 from its origin, just lateral to the symphysis, to its insertion 

 on the posterior horn of the hyoid, near its junction with the 

 body. It tends to pull the hyoid cephalad, or, if the latter be 

 fixed, assists in opening the jaw. 



The mandibulo-hyoid is a thin sheet of muscle tissue having 

 its origin along the inner aspect of the anterior two-thirds of 

 the mandible interdigitating with the mylo-hyoid and insert- 

 ing along the posterior horn of the hyoid. It tends to pull the 

 hyoid cephalad and dorsad, or, if the latter be fixed, it also 

 assists in opening the jaw. 



The sterno-hyoid takes its origin from the upper extremity 

 of the sternum and inserts on the medial third of the posterior 

 horn of the hyoid and proximal portion of the processus 

 retrobasalis. It pulls the hyoid caudad and at the same time 

 slightly ventrad. If the processus retrobasalis be vertical it 

 pulls it back to a horizontal position. (Figs. 3, 4.) 



The omo-hyoid takes its origin from the upper border of 

 the scapula and inserts along the middle third of the posterior 

 horn. It pulls the scapula cephalad and ventrad if the pos- 

 terior horn be fixed. If the scapula be fixed, it pulls the pos- 

 terior horn caudad. (Figs. 3, 4.) 



If both the supra- and infra-hyoid group act simultaneously, 

 the posterior horn is raised ventrad and firmly fixed. The 

 basi-hyal is thus also raised ventrad, allowing a greater free- 

 dom of rotation. This action was noted in lizards under 

 anesthesia, in which the muscles were exposed. 



The third layer consists of the mylo-ceratoid, cerato-hyoid, 

 hyoglossus and mylo-glossus. The mylo-ceratoid takes its 

 origin near the middle of the inner aspect of the mandible, 

 thence running over the pterygoid and inserting along the 

 middle third of the second part of the anterior horn of the 



