MYODOME AND TRIGEMINO-FACIALIS CHAMBER 297 
the Mammalia monotremata and of lower vertebrates. Gaupp 
had previously suggested that the trabecula had here simply 
‘cut through’ the artery, but Voit is not inclined to accept this 
suggestion. The bounding walls of this foramen are, however, 
under my interpretation of the conditions, of parachordal (polar) 
and not of trabecular origin, and there is, accordingly, no 
question here of its lying on one side or the other of the trabec- 
ula. It does, however, apparently lie lateral to the polar ecar- 
tilage, and hence morphologically lateral, instead of mesial, to 
the trabecula, and a possible explanation of this will be given 
when the polar cartilages are considered later. 
The processus pterygoideus arises from the ala temporalis at 
the base of its lamina ascendens, and hence, under my inter- 
pretation of the conditions, from the ventral edge of the lateral 
wall of the trigemino-facialis recess. Its position, alone, thus 
indicates that it is a remnant of the lateral wall of the pars jugu- 
laris of a trigemino-facialis chamber, and its relations to the 
nerves, arteries, and veins are in accord with this conclusion. 
The several branches of the nervus trigeminus all lie dorsal to 
it, as they should; the nervus petrosus superficialis major runs 
forward ventral to it; and the vena capitis media of embryos 
must necessarily have passed dorsal to the place where the proc- 
ess later develops, for that vein lies directly ventral to the ner- 
vus trigeminus. The relations of the arteria maxillaris interna 
(carotis externa of fishes) to the process vary. In embryos of 
the rabbit the artery perforates the process (Voit). In embryos 
of the dog it is said by Olmstead (’11) to traverse a canalis alaris 
s. alisphenoideum, which begins on the external surface of the 
lamina ascendens of the ala temporalis and issues on its anterior 
edge. The foramen rotundum opens into this canal, and the 
second branch of the trigeminus, passing through this foramen, 
enters the canalis alaris and, accompanying the arteria maxil- 
laris interna, issues through its anterior opening into the orbit. 
In Vespertilio the artery is said by Grosser (’01) to enter the 
cranial cavity through the foramen ovale, then to run forward 
ventral to the second branch of the trigeminus, and to issue from 
the cranial cavity through an opening which corresponds to the 
