ANATOMY OF BALDEN OPTERA ROSTRATA. 
231 
Proceeding from within outwards the muscles of the tongue were arranged in the fol- 
lowing order, on either side of the well-developed, central, cellular raphe. 
First. The Genioglossus, which was irregularly quadrilateral in outline and arose 
from the internal border of the inferior maxilla near its anterior or symphysial extre- 
mity ; the fibres ran upwards and inwards, forming a thin flat belly to be inserted into 
the deep surface of the mucous membrane in the centre of the tongue. 
Second. The Lingualis, or intrinsic muscle of the tongue, consisted of several series 
of interlacing muscular fibres running both in a transverse and longitudinal direction, 
which together contributed to form a considerable portion of the hulk of the organ ; 
the longitudinal part lay between the genioglossus and the hyoglossus muscles ; the 
transverse fibres decussated with the fibres of the other muscles of the tongue. 
A vertical series of lingualis fibres were found interposed between the lingual artery 
and the hyoglossus muscle, separating the latter from the other sets of intrinsic fibres. 
Third. The Hyoglossus arose by a round fleshy mass from the great cornu of the 
hyoid bone, from whence it ran forwards expanding in its course, and Was inserted into 
the entire length of the side of the tongue from base to tip. 
Fourth. The Palatoglossus formed the orbicular sphincter surrounding the isthmus 
faucium, and was exposed by removing the mucous membrane from the buccal 
surface of the lateral boundaries of this opening ; it was a strong crescentic muscle -f 
of an inch in thickness, 2 inches in breadth, and about 3^ inches in length, measured 
from the tongue to the middle line of the velum palati ; it arose from the median line 
of the soft palate, and its fibres passed downwards and outwards in an arched direction 
to be inserted into the dorsum of the tongue, on a plane external to the insertion of the 
last-described muscle. 
The Palatoglossus, from its position, was evidently of great importance in the economy 
of the animal, as by its contraction it completely closed the isthmus faucium and so 
prevented the entrance of water into the oesophagus during the prehension of food ; it 
likewise cut off the passage of air through the mouth during the act of respiration. 
Fifth. A thin expanded muscular plane external to the hyoglossus existed as a 
representative of the Styloglossus ; it arose from the outer side of the fibro cartilage, 
which united the styloid bone or cornu of the os hyoides to the base of the skull, lying 
external to all the other muscles of the organ ; its insertion extended forwards into the 
posterior half of the lateral margin of the tongue. 
From the arrangement of the preceding muscles, the following conclusions may, we 
think, be deduced with respect to the motions of the tongue. Although fixed to the 
floor of the mouth, its sides could most probably be elevated by the contraction of stylo- 
glossus and palatoglossus muscles, and centrally depressed by the genioglossus and 
hyoglossus, thus rendering it transversely concave on the upper surface, especially 
towards the base ; its apex might likewise be depressed, as in prehension, by the genio- 
glossus, and its base, during the act of deglutition, might be lowered by the hyoglossus 
and depressor muscles of the hyoid bone. Its body might be shortened by the lingualis 
