914 
MR. A. FRASER ON THE DEVELOPMENT OF THE 
sidered that the function of the pessulus was to prevent the stapes from falling into 
the vestibule. 
In the Mammalian embryoes from which my sections have been made, there are two 
forms of this artery, one which disappears very early represented by the embryoes of the 
Pig, Dog, Sheep, Calf, and Human subject; the other which persists throughout life as in 
the embryoes of the Hat—the former may be called arteria stapedialis, the latter arteria 
stapedio-maxillaris, a name already applied to it by Hyrtl in the adult. In embryoes of 
the Rat the artery has the following course (Plate 56, figs. 22 and 24):—The carotis 
communis, when it approaches the ventral part of the cartilaginous wall of the cochlea, 
divides into two branches, one considerably in front of the other, passes internal to the 
cochlear wall on its way to the brain cavity, and corresponds to carotis interna; the other 
passes external to the wall of the cochlea, dorsad of and slightly internal to the sulcus 
tympanicus, through the embryonic ring of the stapes, threading it, as it were, then 
passes ventrad of the seventh nerve, external to its ganglion, internal to the mandibular 
division of the fifth nerve, then comes into relation with its maxillary division, and 
runs underneath this nerve in the whole of its extent until it terminates in branches to 
the face. During this course it gives off several small branches, which pass in various 
directions, one of which, however, passes into the mandibular arch. The artery in the 
embryoes of the Pig, which may be taken to represent those in which it early dis¬ 
appears, has the same course from the carotis communis through the ring of the stapes 
upwards as far as the ganglion of the seventh nerve, where it divides into two small 
branches (Plate 54, fig. 6), which pass external to the gasserian ganglion, and beyond 
which I have failed to trace them. In the adult Rat it is a large and important artery 
and has the following course:—The carotis communis is a long straight artery, and runs 
from the aorta to the upper part of the air tube ; it there divides into two branches, 
the external of which passes up over the outer surface of the mandible, forming the 
arteria facialis ; the internal is a short vessel, which soon divides into two branches, the 
internal of which passes between the anterior Eustachian thickened portion of the 
bulla arid the basisphenoid on its way to the brain cavity, and corresponds to carotis 
interna ; the external and larger of the two branches passes through a foramen formed 
in the line of articulation between the hinder part of the bulla and the petrosal into 
the tympanic cavity, then passes up in front of the fenestra rotunda, grooving the 
cochlear wall, between the crura of the stapes, over the cerebral surface of the bulla, 
through a foramen in the alisphenoid, then runs under the maxillary division of the 
fifth nerve in the whole of its length until it terminates in branches to the face, corre¬ 
sponding, in the latter part of its course, to the infra-orbital artery in the human 
subject. This artery, then, plays a very important part in the formation of this per¬ 
forated ossiculum; in truth, it bears the same relation to the stapes that the embryonic 
vertebral artery does to the cartilaginous transverse processes of the cervical vertebrae, 
or that any artery bears to a cartilaginous mass through which it has to pass, that is, 
it leaves a foramen. Hence it is a fair deduction that in all Mammalia possessed of a 
