212 ON THE ANATOMY OF THE INDIAN DARTER. _ [Feb 7, 
no further flexion is possible. The 8th vertebra is thus so articulated 
with the 7th anteriorly and the 9th posteriorly as to allow it, when 
the neck is flexed, to be nearly at right angles to the rest of the 
neck, the two portions of which, though parallel, are then at different 
horizons, something like the two bars of a parallel ruler (vide diagram, 
p- 211, fig. 1). When the neck is bent in this Z-shaped form, any 
opening out of the anterior angular bend by the action of the’ 
anterior neck-muscles causes the anterior moiety of the neck to 
suddenly shoot out, thus causing a corresponding protrusion of the 
head and beak (diagram, fig. 2). By the flexion of the 6th on the 
7th, and of the 9th on the 10th, cervical vertebrze, the curve of the 
neck is increased—the articulations of the 8th vertebra still forming 
the double hinge round which motion takes place—and the impaling 
action correspondingly augmented. This protrusion, though only 
for a short distance, is so violent as to effectually ‘strike ’”’ the fish 
which the bird is pursuing. 
The bending-back of the neck is effected, partly by the action of 
the longus colli posterior, partly by a special pair of closely approxi- 
mated muscles, situated anteriorly along the middle line of the neck, 
which arise close together from the hemapophysial spine of the 
11th cervical vertebra, near its anterior articular end, and are in- 
serted into the sides of the anterior half of the 6th cervical. 
The opening-out, on the other hand, of the genu formed by 
the 7th and 8th cervicals—by which, as already described, the 
impaling action is produced—is caused by the contraction of the tho- 
racically very powerful longus colli anterior. The main tendon of 
this is inserted on the long, backwardly-directed hemapophysis of 
the 8th cervical, playing round the doubly-grooved surface of the 
inferior arch formed by the hemapophyses of the 9th cervical, to 
which yertebra, as well as to the 10th, it gives off much smaller ten- 
dinous slips. 
It is obvious that considerable advantage is gained by the action 
in question, the rapid protrusion of the narrow neck and head over 
a small space by this mechanism necessitating a less amount of 
exertion than would a similar movement of the whole bird over the 
same space, and being equally efficacious in striking the prey. The 
whole mechanism, it may be observed, exists ina less developed form 
in the neck of the Herons, Cormorants, &c.; and it requires but a slight 
modification of the arrangement of these parts in those birds—none 
of which, so far as I know, impale their prey like the Darters—to 
bring about the perfect adaptation of these structures to a newly 
acquired mode of feeding. 
