OSSICULA AUDITUS IN THE HIGHER MAMMALIA. 
905 
incus, the latter being attached by embryonic tissue to the upper extremity of the 
hyoidean cartilage. The short crus, later in its appearance, is described as growing 
backwards from the body. The median thickening forms the malleus, while its down¬ 
growing' process forms the neck and manubrium. The anterior thickening soon dis¬ 
appears and has no significance. The separation between the posterior and median 
thickenings is complete in embryoes measuring 2*7 centims. The union between the 
long crus of the incus and the upper end of the hyoidean cartilage is described as being 
secondary. The part of the mandibular cartilage which remains after the separation 
of the incus forms the malleus and Meckel’s process. 
The stapes is described as making its appearance first in embryoes measuring 
2*7 centims. At first it forms an accumulation of cells, in the middle of which is seen 
the cross-section of a vessel which he names the arteria mandibularis. He describes 
this as a branch of a vessel which is situated dorsally to the facial nerve, and which he 
calls carotis interna. This I shall show further on to be the primitive jugular vein, 
and I shall further demonstrate that the arterial branch does not go to the mandible. 
The stapes is also described as being independent of the cartilages of the two first 
post-oral arches and of the periotic capsule. 
These various and conflicting opinions may be reduced to order as follows :—All 
observers are agreed that the malleus has its origin in the mandibular cartilage ; that 
the incus is either the proximal extremity of the mandibular cartilage or the proximal 
extremity of the hyoidean cartilage; that the stapes has its origin in the mandibular 
or the hyoidean cartilage, or is a bud from the periotic capsule, or built independently 
round a small artery. 
PERSONAL WORK. 
Methods of Preparation, and General Statements. 
The embryoes were prepared after the manner of Kleinenberg ; that is, they were 
placed in his solution of picric acid for periods varying from five to forty-eight hours 
according to size. They were then placed in 50 per cent, alcohol for twenty-four hours, 
then in 75 per cent, for a similar period, and finally in absolute alcohol; stained in his 
solution of hsemotoxylin, placed again in absolute alcohol, then in bergamot oil; 
embedded in a mixture of spermaceti and castor oil, cut, cleared in a mixture of 
creosote and turpentine, and finally mounted in Canada balsam. The embryoes were 
measured by placing their most projecting parts (mid brain and curve of tail) between 
the limbs of a compass, and the length read off on a centimetre scale. 
The work was intended primarily to settle the relation of the incus to the cartilages 
of the mandibular and hyoidean arches, and the relation of the stapes to the hyoidean 
cartilage and the periotic capsule. 
It has been done upon embryoes of the following Mammals. 
Rat embryoes .—The earliest under 8 miilims; then at 8 millims., 1 centim., 1*3 
centim., 2 centims., 2*2 centims., 2*5 centims., 3*5 centims., 4 centims., and at the 
last stage just before birth. 
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