338 B. F. KINGSBURY 



arches, within which branchial coelomic cavities may exist in 

 a niunber of vertebrates (e.g., elastobranchs, turtles) and may 

 appear occasionally in mammals (Froriep, Zimmermann, my- 

 self). In some instances these branchial coelomic cavities are 

 actually or potentially in communication with the pericardial 

 coelom. 



In man and mammals, a number of developmental features 

 serve to modify the more primitive relations of the pharyngeal 

 region. The precocious development of the lungs thus pro- 

 foundly alters the developmental pattern by arising early in 

 the development of the region. If not infrapharyngeal (post- 

 pharyngeal) from their mode of development in the amphibia, 

 they represent the most caudal (7th ?) brancliial pouches. Due 

 to the precocity of their development, the 'intrusion' of the 

 tracheo-puhiionary anlage within the floor of the pharynx is 

 a most marked feature. The early and marked development 

 of the heart correlated with the placental circulation may also 

 be mentioned as altering seemingly in a mechanical way the 

 simpler morphological relations of the region. 



A third factor which modifies the plan of development of the 

 mammalian pharynx is the tongue. Despite the recent state- 

 ment by Lewis ('10) that the hypoglossal musculature develops 

 from mesenchyme in situ, it seems highly probable although 

 not yet actually demonstrated — that the myoblasts are directly 

 derived from the first three (or four) myotomes and occupy 

 secondarily the hypobranchial region; differently put, that the 

 pharyngeal region is primarily cephalad of this musculature and 

 in its developmental differentiation and expansion caudally 

 there is a mutual shifting which brings about the characteristic 

 intrusion of the hypoglossal musculatm-e and the development 

 of the tongue. The course and relations of the hypoglassal 

 nerve have thus a marked morphological value. Inasmuch 

 as a hypobranchial musculature is present throughout vertebrates, 

 beginning with the elasmobranchs — the morphological relations 

 in the cyclostomes being somewhat problematic — it is clear that 

 in this respect other vertebrates as well as mammals illustrate 

 a departure from the primitive pharynx morphology. How- 



