908 
MR. A. ERASER ON THE DEVELOPMENT OE THE 
tliG cai tila^es is common to the embryoes of the human subject and 
the lower animals; but while in the embryoes of the lower animals the nerve never 
comes into relation with the incus; in the human embryo it has the same relation to 
the long crus (Plate 55, fig. 16) as to the hyoidean cartilage. This relation, if not 
secondary or acquired, points suggestively to the origin of the incus. The mandibular 
branch and the trunk of the seventh have been described as being homologous to the 
maxillary and mandibular branches of the fifth, but the mandibular branch of the 
seventh differs from the maxillary division of the fifth in not being ganglionic at its 
origin and in joining the mandibular division of that nerve. 
In sections of embryoes before birth the trunk of the seventh has acquired its 
characteristic adult course (Plate 58, fig. 36) ; that is to say, the anterior portion of 
the trunk is pushed in a ventral direction by the growth chiefly of the cochlear part 
of the labyrinth. 
The primitive jugular vein in the earliest embryoes is of very large size, being the 
most conspicuous feature in the sections. It returns the blood from the entire head. 
It lies dorsad of the gasserian ganglion and seventh nerve, ventrad of the periotic 
capsule, and then passes backwards towards the heart (Plate 54, figs. 3-6 ; Plate 55, 
figs. 17, 18 ; Plate 56, figs. 20, 22, 24 ; and Plate 58, fig. 39). This is the vein that 
Salensky names arteria carotis interna. It has the same relations as the cardinal 
vein in the Chicks head. When the ossicula begin to develope it commences to 
disappear, and is soon replaced by the internal and external jug ula r veins. 
In the earliest condition of the hyomandibular cleft in the dorsal region, the hypo¬ 
blast lining approaches and touches the external epiblast. I feel convinced that this 
cleft never actually forms a perforation in this region (region of membrana tympani), 
although it is perforated ventrad of this. Should the above supposition be correct, 
the formation of the membrana tympani would be very easy to understand; the 
hypoblast lining forming the mucous lining of the adult membrane, the epiblast the 
cuticular covering, while the fibrous layer is derived from the ingrowth of mesoblast, 
which along with the proximal extremity of the mandibular cartilage separates these 
two layers from each other (Plate 55, fig. 18; Plate 56, figs. 23, 26; and Plate 57, 
fig. 29). In the oldest embryoes the manubrium mallei occupies the entire space 
between the dorsal part of the cleft and the bottom of the meatus auditorius externus 
(Plate 55, fig. 13 ; and Plate 57, fig. 31). 
His (17) has recently raised doubts as to the correctness of the usually accepted 
statements first advanced by Rathke and Huschke regarding the open condition of 
the clefts. These authors passed bristles from the external surface through the clefts, 
and as they appeared in the cavity of the pharynx, they concluded that the clefts were 
open. His, on the contrary, states that the bristles were passed through the delicate 
epiblast and hypoblast, which come into close contact with each other. He does not 
press his observations, but leaves them as matter for future determination. 
The dorsal and external part of the cleft, following Moldenhauer ( 18 ), may be 
