498 
MR. OSLER’S OBSERVATIONS ON THE ANATOMY 
111 the descriptions I have to offer, and in the drawings by which they are 
illustrated, I propose to guide the naturalist through the successive stages of a 
dissection which may enable him, without much difficulty, to display the parts 
for himself. Where the subjects are so very small, no care will always pre- 
vent oversights, and even errors ; and after every precaution to ensure accu- 
racy, it is probable that I may be corrected in some points by naturalists who 
enjoy opportunities for dissecting recent specimens of the larger tropical mol- 
lusca. I wish therefore to show how the different parts may be displayed 
without injury ; or at least, by what mode of dissection I have arrived at my 
own conclusions. 
The herbivorous mollusca which I have examined have three distinct modes 
of feeding. They browse with opposite horizontal jaws — they rasp their food 
with an armed tongue, stretched over an elastic and moveable support — or 
they gorge it entire. Trochus crassus is a convenient example of the first ; 
Turbo littoreus of the second ; and Patella vulgata of the third. 
Trochus crassus is furnished with a pair of cartilaginous jaws, whose supe- 
rior margins are thickened and rounded ; and which are so united by a liga- 
ment along their inferior edges, that they open and close like a book. A small 
accessory cartilage is loosely connected by alignment to the posterior extremity 
of each. Between the jaws, and extending about half an inch beyond them, is 
the tongue, not flat, as in Turbo, and Patella, but folded into a semi-cylinder, 
and whose margins are furnished with a membrane which is expanded over 
the rounded upper edges of the jaws. The tongue is armed on either side with 
a series of imbricated and lamellar teeth, waved like an Italic^ set in a direc- 
tion obliquely forward and downward, and whose serrated edges incline back- 
ward. The space between these opposite series, which forms about two fifths 
of the breadth of the tongue, is set with corresponding transverse rows of 
small sharp teeth, whose points have a direction similar to that of the lamellar 
ones. The tongue, thus arming the opposite jaws, is secured in its place by 
the lingual membrane, and by the muscles inserted into it. 
The movements of the jaws and tongue are effected by three sets of muscles. 
The first of these (Plate XIV. b, fig. 2 and 3.) occupy all the face of the jaw, 
and are inserted along the lingual membrane, and around the inferior half of 
the mouth. Their lowermost fibres on either side, inserted into the extremity 
