STERNA HIRUNDO, COMMON TERN. 



683 



B. — S. hinitido ex Amo'icd. 



* Inches and hundredths. 



Anatmniral characters. — The month is only moderately large, it being exceedingly 

 narrow anteriorly, and only widening toward the fauces, where, however, the diverg- 

 ence of the tomia gives it considerable breadth. The palate is concave autero-posteri- 

 orly, but is nearly flat laterally. It is soft and vascular only for about two-thirds its 

 length, the anterior third being corneous, and being merely a deep, narrow, longitud- 

 inal depression for the reception of the closely-approximated rami of the inferior max- 

 illa. This single depression bifurcates about three-fourths of an inch from the tip, and 

 for the rest t f the extent of the palate there is a deep depression on each side, just 

 within the superior tomia and zygonuv. for the reception of the devaricating rami of 

 the inferior mnxilla. On the median liue there is a slightly marked ridge, very short, 

 however, and quickly bifurcating to form the tissure of the posterior nares. The edges 

 of this median elevation, on which the u.ires open, are beset with a single row of small 

 obtuse iiapillic. On either side of the median line is a longitudinal sulcus, which sep- 

 arates a lateral longitudinal ridge, which is beset posteriorly with more prominent and 

 acniely-pointed papillae These various ridges and sulci all terminate in papillated 

 extremities. Beyoml them the palate is (juite smooth, somewhat vaulted, still divided 

 in two by the backward coutiuuance of the nasal tissure. This vaulted portion is 

 bounded posteriorly by two obliquely-placed curved rows of small acute papillae, con- 

 taining between them an oval ibramen, the opening of the Eustachian tube. 



The floor of the mouth has the form of an elongated, narrow isosceles triangle with 

 concave sides. The rami are so closely approximated from the commencement of the 

 symphysis as merely to leave room for the reception of the tfsngue. The floor of tho 

 mouth, though dilatable, is not so much so as in the other subfamilies, and the soft 

 niendjranes terminate fully an inch from the tip. The tongue arises about oppo- 

 site! the termination of the feathers on the side of the mandible. It measures au 

 inch and a (piarter in length ; it is exceedingly slender throughout its whole length, 

 and tapers to a very line and acute ajiex, which is not bilid. It is soft and fleshy only 

 for a third of its length, the remainder being quite corneous. Its dorsum has a pretty 

 well-marked longitudinal sulcus. It terminates posteriorly in an elevated, bilid, papil- 

 lated extremity, tlie ends of the cornua being free and projecting. The rima glotlidis 

 begins about a third of an inch from the end of the tongue, and is two-tenths of an 

 inch long. It has no papilUe along its edges, Ijut its termination is paiiillati', aiul a 

 row of pajiilla' extend transversely on eitlier side. Near the angle of the mouth the 

 mucous iiiend)rane is thrown uj) into irregular folds, the begnining of the regular 

 longitudinal (esophageal ones. The disposition of the muscular layers of the floor of 

 th(^ mouth jiiesents nothing peculiar. 



Tile u'sophagus measures about four inches in total length, including the proven- 

 trieulus. It is of ])r(!tty uniform diameter throughout, but enlarges a little toward its 

 termination; but the jiroventriculus is the direct continuation of it, and is not sud- 

 d(Mily nor I'otably larger than the gullet itself It is, as usual, capable of great dis- 

 tension. When undistcnded, the niiu ous nu inbrane is tlirow)i up into numerous longi- 

 tudinal I'olds, quite straight except just at the commencement of the tube, where they 

 are .sonu'what waved. The canal lias evidently great contractile power, from the 

 thickness of tho two layers of muscular libres which inclo.se it. 



The belt of proventricular glands is aboul a third of an inch broad. They form an 

 uniuterrui>ted /.one (|uitt^ around the cireumfereiiee of the canal, the niaigin of the 

 girdle being str.iiglit and w<'ll driiiied. The color of the mucous membrane is here 

 darker than elsewiiere, and has also a dill'ereiiee of texture <|iiile appreeialdo to the 

 ii.-iked eye and to I lie touch. Tne oiilices of the solvent glands may be seen as minute 

 l)un(lures, si'attered thickly aiul t \<'nly over the whole suiface. 



The gigerium is very small, not larger in external circumference than the jiroven- 

 tiieulus. It suiiervenes w itiiout any interval, .and witliout any change of dinetion, 

 directly upon the proventrieulus, with which it communicates by a large oriflce. It 



