330 ON THE ANATOMY OF THE INDIAN DAETER. 



different horizons, something like the two bars of a parallel ruler (vide 

 diagram, fig. 1, p. 329). 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 vertebrae, 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 aug- 

 mented. 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 approximated 

 muscles, situated anteriorly along the middle line of the neck, which 

 rise close together from the haemapophysial spine of the llth cervical 

 vertebra, near its anterior articular end, and are inserted 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 thoracically very powerful 

 longus colli anterior. The main tendon of this is inserted on the long, 

 backwardly-directed haemapophysis of the 8th cervical, playing round 

 the doubly-grooved surface of the inferior arch formed by the haemapo- 

 physes of the 9th cervical, to which vertebra, as well as to the 10th, it 

 gives off much smaller tendinous 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 in a 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. 



