452 CETACEA. 



margin is thin. Two strong tendinous retractor muscles, two inches in length, are 

 prolonged forwards and upwards from the anterior margin of the posterior nares along 

 the floor of the sac and appear to be attached to the posterior palatine process of 

 the pterygoids. They are separated by an interval anteriorly, but unite posteriorly 

 and surround the margin of the orifice like a sphincter. The whole surface of this 

 sac, from the orifice forwards to the narial septum, is richly covered with the orifices 

 of small mucous glands (PL XXVIII, ^g. 3) . The surface also of the sac-like 

 portion is thrown into strong tendinous bands or folds, resembling chordce tendinece. 

 In all the specimens I have examined there are indications, more or less distinct, on 

 the lateral walls of the sac of nearly longitudinal tendinous bands separated from 

 each other by intervals varying from 0*25 inch to nearly an inch in extent, these 

 interspaces being divided into long arched crypts varying in size and number and 

 disposed more or less vertically. In one of these crypts the Eustachian tube (Eig. 3, 

 eu^) seems to open. 



Eustachian Tube. — The opening to this tube (rf) appears, as I have just 

 said, to be situated in the posterior nares, — at least the only orifice communicating 

 with the canal that I have been able to perceive is situated in that locality. The 

 opening is placed on the lateral wall of the nares, 0'75 of an inch above the narial 

 rima in an adult in which I had no difficulty in detecting the orifices and to the 

 position of which I had been led by what I had observed in a semi-adult indivi- 

 dual. I must state, however, that it was a matter of considerable difficulty to 

 find the orifice in the last-mentioned specimen, but that its presence in the adult 

 and in the position indicated was easily demonstrated. In looking into the post- 

 narial pharyngeal sac or dilatation of the Eustachian tube in the semi-adult, a patu- 

 lous diverticulum from the external wall of the sac, near its anterior end, was observed 

 to pass outwards in the direction of the wall of the posterior nares : but on attempt- 

 ing to pass a probe along this, its progress was impeded by valvular folds of the walls 

 of the passage. On directing my attention, however, to the external wall of the pos- 

 terior nares I found that the probe passed along one of the crypts {eu^) and ran 

 upwards, and on introducing the probe again from the sac I found it appearing on 

 the posterior nares through the crypt in question. In the adult I passed no probes, 

 but observing an oval orifice in about the same position as the crypt, I slit open its 

 upper margin and found it to constitute a canal {d) which ran upwards and was 

 about half an inch in length and a quarter in breadth, and, at the former distance 

 from the opening, the outer wall of the passage abruptly stopped as a crescentic 

 fold, the inner or narial wall being prolonged upwards for 0*40 inch beyond it, so that 

 an elongated slit occurred in this position opening into a considerable cavity. 

 This was found to result from the union of the Eustachian tube with its long 

 posterior prolongation or guttural pouch, thus forming a cavity common to 

 both, and which sends up valvular passages around the sac of the Eustachian 

 orifice which is placed opposite to the end of its tube (PL XXVIII, fig. 3). The 

 postnarial end {pn) of the Eustachian tube and the commencement of the guttural 

 pouch are each protected by thin folds of membrane which must act more or less 



