PROFESSOR OWEN ON THE EUSTACHIAN CANALS IN CROCODILES. 
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the outlet for the hypoglossal and eighth pair of nerves, ^ and j). In a young Crocodile, 
with a head of eleven inches in length, the common trunk, fig. 2, cc, of both carotids 
is continued along the under surface of the cervical vertebrae as far as the dentata, 
where it bifurcates into the two carotids : these diverge, ascend, inosculate with the 
vertebral artery, v, and subdivide into the ectocarotid, ec, and entocarotid. The latter 
artery, c, at the first part of its course, extends obliquely forwards inwards and up- 
wards, protected by a bony canal, half an inch in length, which terminates by pro- 
jecting freely as a tube of a line in length (Plate XLT. fig. 4, c), opening into the 
cavity of the tympanum beneath the bony plate, 16, to which I have restricted the 
term ‘petrosal*.’ The artery emerging from the bony canal extends forward across 
the base of the tympanic cavity, covered only by a reflexion of its lining membrane, 
for about a third of an inch, and then enters a second bony canal, opening into the 
fore part of the tympanum, and continued to the ‘ sella turcica,’ where the carotid 
enters the cranial cavity, as is shown in Plate XL. fig. 3, c. 
No artery enters the single median foramen, Plate XL. fig. 1, e, situated close 
to the suture between the basioccipital and basisphenoid. The soft palate which 
covers this part, immediately behind the true posterior nares, forms a subcircular pro- 
tuberance with a single central aperture (Plate XLI. fig. 5) ; this aperture is also 
partly closed by a valvular membranous prominence, x, which reduces its area to a 
crescentic form. This orifice in the soft palate is not, as I had supposed, continued 
exclusively from the bony orifice in question, e, immediately above it ; but is the com- 
mon palatal outlet of three canals, one of which, e, is median, extending into the bony 
canal, figs. 6 and 7, e, which ascends into the substance of the basisphenoid ; the other 
two, el, are membranous for the extent of eight lines, and diverge as they ascend to 
penetrate the fissures, fig. 7j el, one on each side of the larger median foramen, and 
which lead to canals, fig. 7, el’, extending upwards between the basioccipital and basi- 
sphenoid. 
From the inferior openings, Plate XL. fig. 1, el, of these canals in the dry skull, 
grooves lodging their membranous prolongations are continued to the common me- 
dian fossa into which the middle osseous canal, fig. 7? e', opens by the foramen, e, in 
question. Dissections of the recent parts demonstrated that this foramen, like the 
two lateral canals, communicated by a membranous tube (fig. 5, e) with the surface 
of the palate and would receive air from the mouth. It was next to be determined 
where the air would be conducted by those tubes ; and the passage leading from the 
median foramen was first traced. In an alligator with a head 14 inches in length, 
the foramen, e, leads to a canal lined by a continuation of the palatal membrane, 
which ascends along the suture between the basioccipital and basisphenoid, for 
nearly 2 inches, and then bifurcates ; one branch inclining forward into the basi- 
sphenoid, the other rising vertically into the basioccipital, and both in the same 
* It -was probably the observation of this structure in the dry skull that misled the continuators of Cuvier 
into the belief that the canal, c, was the osseous part of the Eustachian tube. 
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