OSSICULA ATJDITUS IN THE HIGHER MAMMALIA. 
911 
towards the ventral, and forming the elements of the neck and manubrium of the 
malleus, while that of the hyoidean had its concavity directed towards the mandibular, 
to which it closely applied itself. The proximal extremity of this cartilage forms the 
head of the incus, the long crus in the majority of embryoes, those of the Pig especially, 
being continuous with the rest of the cartilage (Plate 54, fig. 5), but in some Dog and 
Pabbit embryoes there was a slight gap between the long crus and the remainder of the 
cartilage (Plate 54, fig. 4) ; passing dorsally from the head of the incus is a short 
process (slightly exaggerated in Plate 54, fig. 5) which eventually becomes the short 
crus of the incus. 
The long crus has at this stage no bend inwards towards the stapedial ring (Plate 56, 
fig. 24). The distal end of the hyoidean cartilage is closely connected to the cartilage 
of the first branchial arch (thyro-hyal), so much so that if microscopic sectional 
appearances were alone to be considered they could be described as being continuous. 
The drawings do not do justice to the immature condition of these cartilages, there 
being no sharp limiting lines in nature. In older embryoes there is a striking similarity 
in the appearance of the cartilages in the different embryoes (at the same developmental 
stage), Plate 54, figs. 8 and 9 ; and Plate 55, fig. 10, for the Pig; Plate 55, fig. 18 ; and 
Plate 56, fig. 19, for the Sheep ; Plate 56, fig. 21, for the Dog ; and Plate 56, figs. 25 and 
26 ; and Plate 57, fig. 27, for the Pat. In the entire series the several parts of the 
malleus and incus can be readily distinguished; the apex of the long crus of the incus 
has but a slight turn inwards towards the stapedial ring (Plate 54, figs. 7 and 9 ; Plate 55, 
fig. 18; and Plate 57, fig. 27), and it is separated from the remainder of the cartilage 
(which joins the periotic process of the periotic capsule) by a slight interval, but it 
agrees with the cartilage both in its form and general direction in a very marked 
manner. It also, and this is equally important, agrees with the hyoidean cartilage 
in every histological particular; it takes up the colouring matter in the same way, 
and its cells assume the hyaline character at the same period of time—those of the 
mandibular cartilage having undergone that change at an earlier date. 
The seventh nerve and its chorda tympani, or mandibular branch, have the relations 
to the cartilages already described. In still older embryoes (Plate 55, figs. 13, 14, 
15, and 16, for Human embryo; Plate 57, figs. 29, 30, 31, 32, 33, 34; and Plate 58, 
figs. 35, 36, 37, 38, for the Pat) the individual parts of the adult ossicula are fully 
developed. The joint between the malleus and incus is now for the first time clearly 
evident, and its V-shape is worthy of notice (Plate 58, fig. 36). The manubrium is 
large, and of the same shape as in the adult; it occupies the entire space between the 
sulcus tympanicus and the meatus auditorius externus (Plate 55, fig. 13 ; and Plate 57, 
fig. 31); at its junction with the neck is a well marked process, which I have called 
posterior (Doran’s (19) orbicular process or apophysis—a bad name, because of the 
orbicular apophysis of the incus).. The processus muscularis of Hyrtl and the tensor 
tympani muscle are well developed. 
6 A 
MDCCCLXXXII. 
