42 GENERAL EMBRYOLOGY. 
intermedium helicis. The upper tubercle on the hyoid arch is the tuberculum 
anthelicis, the middle is the tuberculum antitragicum, and the lowest is the 
tuberculum lobulare. Shortly after the appearance of the tubercles a process, the 
caudal process, grows backwards and downwards, from the posterior part of the 
tuberculum intermedium helicis, behind the tuberculum anthelicis and the tuber- 
culum antitragicum to the tuberculum lobulare, with which it fuses. The 
tuberculum tragicum remains more or less distinct, and it forms the prominence 
ealled the tragus which les in front of the concha and external auditory meatus. 
The two tubercles of the helix and the caudal process unite to form the helix 
or marginal portion of the pinna; this terminates below in the lobule which 
is developed from the tuberculum lobulare. The tuberculum anthelicis and the 
tuberculum antitragicum are the rudiments respectively of the antihelix and the 
antitragus, and 
the latter unites 
below the lower 
part of the cleft 
withtherudiment 
of the tragus, 
forming the lower 
boundary of the 
outer part of the 
external meatus. 
It shouldaiie 
noted that in the 
early stages the 
tuberculum — an- 
terius helicis hes 
in front of the 
outer part of the 
first visceral cleft, 
but it does not 
retain this posi- 
tion in the later 
stages during 
which the cleft 
is relatively re- 
HM 
oe fo, - ay Ae . duced in size, and 
1c. 34. FIGURES, MODIFIED FROM His, ILLUSTRATING THE FORMATION OF 
nee 2 ee cae when develop- 
1. Tuberculum tragicum = Tragus. 6.  Tuberculum antitragicum = Anti- ment iscompleted 
2. ws anterius helicis | tragus. and theouter part 
3. Me ep _intermedium helicis } Helix. 7. Tubereulum lobulare= Lobule. of the cleft is 
4, Cauda helicis HM. Hyo-mandibular cleft. 5 for a 
5. Tuberculum anthelicis = Antihelix. OY. Otic vesicle. transformed into: 
the external audi- 
tory meatus the commencement of the helix, which is developed from the tuberculum 
anterius helicis, is situated just above the outer extremity of the external meatus. 
The outer part of the cleft is moulded into the external auditory passage. It 
remains relatively shallow and devoid of bony boundaries till after birth, but in 
the subcutaneous tissue round the lower margin of the tympanic membrane an 
incomplete ring of bone is formed during the third month, and at an earlier period, 
above the upper part of that membrane, the rudiment of the squamous part of the 
temporal bone appears. To the outer side of the tympanic ring in the subcutaneous 
tissue of the pinna and the outer part of the external auditory passage three pieces 
of cartilage appear, and they afterwards join to form the cartilage of the pinna and 
the external auditory meatus. 
After birth the external meatus is deepened, by the outgrowth of the tympanic 
ring below and of the squamous part of the temporal bone above, together with a 
coincident increase of the outer part of the canal. 
The tympanic cavity and the Eustachian tube are both formed from the inner 
part of the first visceral cleft, and consequently they are both lined by entoderm. 
