718 MANUAL OF PHYSIOLOGY. 



and the buccal cavity below. The palate when complete in 

 front gradually closes toward the back of the buccal cavity, 

 and here the communication between the nose and the pharynx 

 is left. 



Imperfect development of these parts gives rise to the common 

 congenital deformities, cleft palate and hare lip. 



The first cleft is the hyo-mandibular ; it forms the tympano- 

 Eustachian cavity, which becomes separated from the surface by 

 the closure of its outer end by the growth of the membrana 

 tympani, the external auditory meatus and ear being formed 

 by an outgrowth of the tissue surrounding the tympanic mem- 

 brane. 



The mandibular arch contains, close to its connection with the 

 superior maxillary process, a rod of cartilage, called Meckel's 

 cartilage. This becomes partly converted into the malleus, partly 

 into the internal lateral ligaments of the temporo-maxillary ar- 

 ticulation. 



The second, or hyoid arch, gives origin to the incus, the stylo- 

 hyoid process and ligament, together with the lesser wings of the 

 hyoid bone. 



From the third arch arise the body and greater wings of the 

 hyoid bone together with the thyroid cartilage. 



