88 DAVIDSON BLACK 



distribution of the motor VII nerve is relatively constant, that 

 of the motor IX may be quite variable so that a simple consider- 

 ation of the peripheral distribution of their nerves gives no hint 

 of the possible underlying cause of the central association of their 

 motor nuclei. 



From the functional standpoint, however, facts may be adduced 

 Avhich seem to have some bearing upon this question. Among 

 reptiles for the first time in phylogeny pulmonary ventilation 

 may be carried on independently of the hyobranchial pump 

 mechanism, so that in these forms, in contrast to amphibians, 

 the glottis may remain open throughout the whole cycle of 

 pulmonary respiration. Closure of the glottis is, however, neces- 

 sary during deglutition in all reptiles, at least during the first 

 stages of this act. During the whole cycle of pulmonary respi- 

 ration in water-living reptiles (crocodilians and chelonians) the 

 mouth may be kept open while the body is submerged with only 

 the nostrils protruding above the surface. In such animals, 

 therefore, closure of the glottis does not necessarily result through 

 the stimulation of the buccal mucosa innervated by V and VII 

 sensory nerves by water or food. Closure of the glottis does 

 take place, however, when such stimulation reaches the mucosa 

 of the VII-IX sensory area and when at the same time the bucco- 

 pharyngeal muscles are called into play in the first stage of the 

 act of deglutition. The same holds true of land-living reptiles, 

 though in snakes the rima glottidis may be protruded between 

 the two halves of the lower jaw and remain open during the much 

 prolonged act of deglutition (v. Gadow, 1. c). Thus among 

 reptiles for the first time in phylogeny the effectors supplied by 

 the motor IX are no longer muscles of primary respiratory im- 

 portance, but are called into play more especially during the 

 act of swallowing immediately after or at the same time as the 

 VII musculature and as the result of the same stimulation. 



In Rana it was found that the complete separation of the motor 

 VII nucleus from the closely related and caudally placed IX-X 

 motor nuclei w^as apparently a central expression of the changed 

 peripheral relations due to the divorce of the facial musculature 

 from respiratory functions (5, p. 411). In urodeles the retention 



