xxxvi Journal of Comparative Neurology. 



ramus ophthalmicus superficialis, portio facilis and the ramus buccalis. 

 The steps in the development are as follows : 



i). At first it is represented by a triangular plate above the hyoid 

 arch, which is originally connected both with the trigeminus and with 

 the vagus protons, though the connection with the former is early lost , 



2). Simultaneous with the formation of the auditory vesicle it 

 breaks up into auditory and facial divisions. The auditory division 

 enters into intimate contact with the base of the auditory vesicle and 

 the facial division, at the same time, with the epidermis above the 

 hyoid arch and later above the superior edge of the first visceral cleft. 



3). The structure so far is exclusively cellular ; its connection 

 with the brain is by simple contact; fibres pass into the brain later. 



4). Simultaneously with the latter process the facial division sep- 

 arates into ramus ophthalmicus superficialis and ramus buccalis. 



5). The nervus acusticus, ramus hyoideus, ramus buccalis, and ra- 

 mus ophthalmicus superficialis, portio facialis , then constitute four inde- 

 pent branches, each of which has in its central part a ganglion. These 

 united ganglia form a sort of four-pointed star. 



(4). The Vagus group. 



1). It appears first immediately behind the facialis group and in 

 intimate connection with it. 



2). Its cephalic border reaches first the branchial region and pro- 

 longations are successively detached from it, as the visceral sacs are 

 forming, to the third, fourth, etc., branchial arches. The first pro- 

 longation separates before the others and represents the primitive 

 glosso-pharyngeus. Meanwhile the caudal border gives rise to the 

 proton of the spinal ganglia (bandelette ganglionnaire). 



3). Upon the formation of the fourth pair of visceral sacs and the 

 appearance of the somites in the occipital region, the proton of the 

 vagus proper is quite separate cephalad from that of the glosso-pharyn- 

 geus, except at the central part; along the back it is prolonged into 

 the proton of the spinal nerves; below at the level of the notochord it 

 becomes finer and enlarges again lower down in the branchial region. 



4). Subsequently we observe the gradual reduction of the central 

 part next to the brain until only a commissure remains. At the same 

 time the peripheral part develops into the branchial rami and their 

 ganglia and establishes connection with the branchial epidermal 

 thickenings. 



5). The connection, primitively broken, between the proton and 

 the brain is again established, on the one hand by the formation of 

 numerous small roots in the whole region where the proton is adjacent 



