gill-cleft

Almost simultaneously with the formation of the mouth the first gill-cleft breaks through in the fore section of the Amphioxus-embryo

The Evolution of Man — Volume 2 Ernst Heinrich Philipp August Haeckel 1876

Finally, the shell (pinna or concha) and external meatus (passage to the tympanum) of the outer ear are developed in a very simple fashion from the skin that borders the external aperture of the first gill-cleft.

The Evolution of Man — Volume 2 Ernst Heinrich Philipp August Haeckel 1876

At the back part of the head at both sides, near the after brain, a small thickening of the horny plate is formed at the upper end of the second gill-cleft (Figure 2.322 A fl).

The Evolution of Man — Volume 2 Ernst Heinrich Philipp August Haeckel 1876

All these essential parts of the middle ear originate from the first gill-cleft and its surrounding part; in the Selachii this remains throughout life an open squirting-hole, and lies between the first and second gill-arch.

The Evolution of Man — Volume 2 Ernst Heinrich Philipp August Haeckel 1876

Of the four original gill-arches of the mammals the first lies between the primitive mouth and the first gill-cleft.

The Evolution of Man — Volume 2 Ernst Heinrich Philipp August Haeckel 1876

On the left a gill-rod has been struck, and on the right a gill-cleft; consequently on the left we see the whole of a prorenal canal (x), on the right only the section of its fore-leg.

The Evolution of Man — Volume 2 Ernst Heinrich Philipp August Haeckel 1876

In these nothing is left but a relic of the first gill-cleft.

The Evolution of Man — Volume 2 Ernst Heinrich Philipp August Haeckel 1876

The outlying remainder of the first gill-cleft is the rudiment of the external meatus.

The Evolution of Man — Volume 2 Ernst Heinrich Philipp August Haeckel 1876

From the first gill-cleft is formed the tympanic cavity of the ear.

The Evolution of Man — Volume 1 Ernst Heinrich Philipp August Haeckel 1876