The Smooth Facial Muscles of Anura and Salaiuandrina. 335 



lo accordance with the account above given, we may conclude that 

 protraction of the lower jaw is due to the activity of the ptery- 

 goideus muscle. Such a function may in fact be demonstrated by 

 electrical stimulation of the two pterygoidei. 



Retraction of the lower jaw, which immediately follows pro- 

 traction, seems to be provided for in the temporalis. It is doubtful, 

 however, if the assistance of the temporalis is here necessary to the 

 production of this movement, which would probably follow from other 

 causes. Among these causes may be mentioned especially, a) the 

 elasticity of the ligaments at the articulation of the lower jaw with 

 the skull; b) the tension of the m. labialis superior, and c) the 

 elasticity of the intermaxillary apparatus at the rostrum. The elasticity 

 of this apparatus gives rise, as hereafter explained, to the depression 

 of the median part of the palatine portions of the iutermaxillaria. Such 

 depression, however, necessitates also the depression of the tuber- 

 culum praelinguale and an enlargement of the angle between the two 

 partes mentales of the dentalia. These movements, however, involve 

 a backward motion of the dentalia and of the entire lower jaw. 

 Owing to the operation of such forces therefore the retrac- 

 tion of the lower jaw is probably effected without direct 

 participation of the masticatory muscles. 



In Rana pipiens Gmel. and Rana fusca Rös. protraction of the 

 lower jaw seems to be a constant attendant of the inspiratory move- 

 ments, although, as above remarked, it is less conspicuous in quiet 

 respiration, where also it is more or less masked by a movement 

 of the soft upper lip. Occurring at the moment of inspiration, pro- 

 traction of the lower jaw plays an important role in holding the 

 mouth securely closed during the contraction of the bucco-pharyngeal 

 muscles. During protraction the entire arch of the lower 

 jaw is pushed forward in the sulcus marginalis and pressed 

 against the dentary processes of the maxillaria and iuter- 

 maxillaria. In this manner is secured a close contact be- 

 tween the skeletal parts of the jaws and also between the 

 lower jaw and the upper lip. Especially at the rostrum, where 

 the lip and the dentary portions of the iutermaxillaria are strongly 

 incurved, protraction becomes an effective means of holding the 

 jaws together. A second function of protraction will 1)6 described 

 later. 



The glands of the pulvinaria subrostralia and of the integument 

 of the lower jaw supply a secretion, which is forced out during 



